Summary: This passage is divided into two parts. Part one will tell you the whole process that how does a computer get started and what is "boot device not found" while part two will tell you why and teach you how to deal with that when you start your computer.
The error message or the similar, like "boot device not found 3f0 error" in HP and "no bootable device found" in Dell are mostly found on Windows, but Mac users can also catch a glance for knowing more about the computer.
Now, if your computer goes pass the "boot device not found" error and booting up, you can simply test the hard drive using the built-in function of Hardware Diagnostics on your computer. But if the PC just stuck on this error and won't go any further, you need to read on and learn how to fix it.
Part I: What does "boot device not found" mean during starting your computer?
Before knowing that, it's necessary to see how a computer gets started. So that you can better understand and fix the "boot device not found 3f0 error".
A computer is universally started through several stages: (Power the computer and Computer on are not counted as key stages)
Stage 1: Entering BIOS to check Basic I/O information.
When the computer is powered on, the first thing it does is to read ROM chip, where dwells the Basic Input/Output System (BIOS). BIOS then would have a Power-on Self-Test (POST) to check if the hardware can meet the minimum conditions to enable its running. And then, BIOS is to hand over the control to the next initiator. However, before that, BIOS needs to know which drive among the boot devices that have been detected by BIOS is the next initiator's home, and which means BIOS has to make an order to hand over the control, and of course, the higher rank drive gets the priority. That is the so-called Boot Order.
Stage 2: Check and access the Bootloader in the target boot device.
Having handed over the control to a specific drive, the computer will read the first sector of this drive, which is most of the time the first 512 bytes of the drive. The first 512 bytes has its term, "Master Boot Record" (MBR), which clearly records the whole partitions of the drive to help lead the system to the next stage.
Stage 3: Locate the system partition in the target Boot Device.
After the computer has read the MBR of the drive, it goes for a specific partition which stores the data of the OS in the drive and hands over the control to that partition.
Stage 4: Booting from the OS.
Once Mac successfully reads the partition information of the external hard drive, it will go further by calling related programs to recognize the file system of each partition on the external hard drive. A recognized file system will let macOS know how and where your data is stored on the external hard drive, so that it can mount this external hard drive for use.
As the OS lives inside that partition, thus, when the computer hand over the control to the partition, the OS takes over the first chair. Then, the kernel of the OS would be first loaded by the memory, and then all the dark places of the booting process are going to be one by one lighted by the OS, and finally, you will have found that your screen is on.
What does "boot device not found" mean?
Although there is the difference in error messages of different brands of computers, as far as what we have organized from the feedbacks of our users who support different brands, like HP, Dell, Lenovo, and so on, the "boot device not found" means any one or more stages of the whole booting processes are held back, and because of that the computer can't recognize the hard drive to start the operating system.
Part II: Reasons and solutions of "boot device not found"
1. BIOS can't detect the startup drive
Case 1: The drive has poor contact with the motherboard
This happens when you carelessly replace your old HDD with a new SSD or make the part where the drive is quake violently.
How to fix: extract the data line and power wire of your boot device and insert them to the motherboard again.
Case 2: Interface compatibility
This problem sometimes happens like that when you forcibly connect a drive of M.2 NVMe(PCle) SSD to an M.2 SATA SSD interface in the motherboard, or plug the Inter M.2 NVME SSD connector into the ASUS Z97-A motherboard interface, whether they are connected seamlessly or not, your computer will not recognize the boot device, and what's worse is damaging the hardware.
How to fix: have a try on different interfaces on your motherboard and if that doesn't work, replace the drive.
2. BIOS/UEFI sets an incorrect Boot Order
As the computer will get started according to the Boot Order. If the first prior boot device is no longer connected with the computer while you didn't give any change to the Boot Order, then the BIOS/UEFI can't find the device to boot. This often happens when people replace an HDD with a new SSD or start a computer with a non-booting USB Flash Drive or non-booting external hard drive when you have set the "USB Flash Drive" or the "external hard drive" as your first prior Boot Order.
How to fix: correct the Boot Order in the BIOS/UEFI interface depending on which drive you are using to boot your computer now.
3. The startup disk is damaged, unrecognizable, or corrupted
The two stages of stage 2 and stage 3 are bridged through the MBR that is a necessary part of the startup disk. That's to say, anything that makes the MBR damaged, lost, wrong, or unrecognized will ruin both of the two stages at a time, and thus lead to "boot device not found". There are basically 3 possibilities to reach the dilemma.
Possibility 1: The drive is without any operating system
This happens when you replace the HDD in your PC with a new hard drive on the motherboard and the new drive is uninitialized.
How to fix: reinstall the operation system
In this way, you need install an operating system, and store this system in the new drive. During the process of installing an operating system, there will automatically be a hint to ask you to initialize your new drive, and just do as what the hint reads.
Steps to install an operating system, for example, Windows 10:
Step 1. Prepare a Windows 10 USB flash drive/external disk/optical disk and connect it to your computer.
Step 2. Turn on the PC and press the key that opens the boot-device selection menu for the computer, such as the Esc/F10/F12 keys.
Step 3. Select the installation source from the USB flash drive/external disk/optical disk and the installation destination.
Step 4. Install the Setup.
Step 5. Remove the USB flash drive/external disk/optical disk.
Possibility 2: The boot partition is deleted by mistake, the partition table is destroyed, or the boot sign is cleared
How to fix: use some third-party tools, like iBoysoft Data Recovery, to recover your drive data to restart your computer or you reformat your drive and directly reinstall the operation system with private data loss.
Possibility 3: The drive is physically damaged
This happens when the drive falls severely on the ground, the goldfinger is oxidized or the drive is normally and physically aged, making the MBR a bad sector and finally making the boot procedure unable to get started.
How to fix: bad sector of MBR by physical damage is uncurbable for the time being, so you have to turn to another drive.
4. Boot Mode error
There are basically two kinds of Boot Modes: Legacy and UEFI, and these two Boot Mode are incompatible with each other. Windows 7 supports Legacy while Windows 8/10 supports UEFI.
When you upgrade Windows 7 to Windows 8/10, then choose the UEFI Boot Mode in the BIOS interface. However, under this situation, before you reverse the Windows, you need an extra step, changing the partition table of the drive from MBR to GPT, to make sure that the disk is on its best value.
How to change the partition table from MBR to GPT?
You can do that through Disk Management. Firstly, check if there is any partition in the disk. If it is, then the option Convert to GPT Disk will grey out, and you need to delete all the existing partitions (volumes).
Secondly, choose Convert to GPT Disk.
Or through a third-party tool: Aomei Partition Assistant. By using this tool, you don't have to delete any single partition or volume.
When you reverse Windows 8/10 to Windows 7, then choose the Legacy Boot Mode in the BIOS interface and convert your drive from GPT to MBR for the best disk function.
Finally, if you get out of any trouble of "boot device not found" under the help of this article, please follow our YouTube channel. We will provide you more information of high quality at iBoysoft. If you are in trouble with data loss, you can contact us via mailbox at [email protected] Thank you for your kindness.