If you press the Command-Option-Power button to force restart the MacBook Pro but nothing happens, it seems that the Mac can't turn on, there are no graphics on your monitor, no startup chime, no spinning fan, and no drive noise. Your Mac appears to be totally dead.
As you said, "It's plugged into the charger but the A/C adaptor light is blinking and dimmed, " then the power connection could be the reason. If it is a defective adapter, the uncharged Mac can't turn on when the power runs out. So, change a healthy adapter and USB cable, and switch to a working USB port. After charging the Mac for a long time, try to turn on the Mac again.
In addition, when MacBook can't turn on, you can also try the following solutions:
- Disconnect unnecessary peripherals excluding the mouse and keyboard.
- Reset SMC on Intel Mac.
- Perform a power cycle for Intel Macs.
- Try to use an external monitor.
After trying all of the above solutions, if your MacBook Pro still won't switch on or charge, you might think about seeking assistance from nearby Apple Stores, Apple Authorized Service Providers, or independent computer repair shops.
If you successfully turn on the MacBook Pro but find data lost on the drive, try iBoysoft Data Recovery for Mac, professional data recovery software for Mac to recover it.