According to your description, your Micro SD card is highly like suffering from file system corruption or it is failed. In this case, you should use data recovery software to recover your files and replace the failed SD card with a new one. But, before declaring that the Micro SD card has failed, let us first try some simple methods.
Solution 1: Clean your Micro SD card
Long-term use fills your Micro SD card with dirt or dust. You can clean it with a soft cloth or blow the dust off the SD card. If this method does not make sense, consider the alternatives listed below.
Solution 2: Check the connections
When you can't find your Micro SD card on your computer, you should consider if the connections go wrong. You can reconnect your SD card to your computer to check if it is tightly connected. If it is useless, you can try the fixes below:
Fix 1: Unplug the Micro SD card and reconnect it to the other port on your computer.
Fix 2: Connect the Micro SD card to the other PC.
Fix 3: Replace the SD card adapter or reader with a new applicable one.
If simple solutions fail to make your Micro SD card works well, try the following one.
Solutions 3: Recover data and format the Micro Sd card
When an SD card is correctly mounted but not showing on a phone, a likely reason is that the SD card has a file system corruption. You can try iBoysoft Data Recovery Software to scan your files and then format the SD card for later use.
iBoysoft Data Recovery Software is highly recommended with advanced disk scanning and recovery algorithms.
Step 1: Launch iBoysoft Data Recovery and then choose the Data Recovery module.
Step 2: Select the partition where you lost files and click Next to continue.
Step 3: After the scan completes, lost files will be listed.
Step 4: Preview the found files by clicking Preview.
Step 5: Select the needed files and click Recover to start recovery.
Note: If your Micro SD card is not listed after iBoysoft Data Recovery has scanned all partitions, you can use the Find More Partitions function.
How to format your Micro Sd card:
Step 1: Double-click 'My Computer' (or 'This Computer') on the desktop to open it.
Step 2: Select your SD card shown on the panel and right-click it.
Step 3: Click the Format... option, and then a Format panel will pop up.
Step 4: Select a file system, and click Start. Then, wait for your SD card to be formatted.
However, if iBoysoft Data Recovery Software fails to scan your corrupted Micro SD card, then I can determine it is failed. You'd better change another one for your later storage work.