See https://www.raymond.cc/blog/test-your-ram-with-microsoft-windows-memory-diagnostic/ for how to test memory. On Vista and later you can open run, type
mdsched.exe
then click OK, but this is not as thorough check as MemTest86.
You can also run CHKDSK to check the drive for errors. To do that, right-click over the drive in Explorer, choose “Properties”, click the “Tools” tab then “Error checking”.
And you can use the System File Checker tool to repair missing or corrupted system files (sfc / scannow).
But these projects might be damaged somehow. Have you tried exporting each track as a WAV file then importing the WAV into a clean new project?
Have you tried resetting Audacity Preferences?
Gale