Try to reset NVRAM/PRAM to boot your Mac 1. Shut down your Mac 2. Press the power button. Once you hear the startup chime, hold down CMND + OPT + P + R. 3. Hold these until you hear another startup chime, then release them.
Try to do below fixes from your end: 1. Try to plug in different drive or SD card and see if it appears in finder 2. Check the file system format of your SD card. 3. Repair your unreadable SD Card using Disk Utility built0in application First Aid 4. If nothing works, try to recover your data from the SD card as you are left with no choice.
Did you tried booting your Mac in Safe Mode? Also, I will advise you to run Apple Hardware Test to determine a failing Mac component. I am not saying this 100% but the fan might be a problem. Might Be. You better run First Aid and AHT quickly. Keep us posted
If you cannot access your SSD Drive try recovery of the drive using disk utility. Hold command + option + R until progress bar will appear. Choose the Disk Utility and format the new SSD Drive. Meanwhile, check out a similar Solved discussion. It might help you resolve the problem After installing, my SSD is not recognized after a reboot?