Malware

usually after a power failure, the disk system become unstable / corrupted. so when this happens, files on the disk become un-indexed and windows can't find them / access them.

so what you can do is to run the check disk command (chkdsk) from the command prompt. the check disk will reconcile / re-index the files on your disk with the master file table

also, if you have not run a check disk on the computer, then it might be time to do a thorough check by selecting the search and mark bad sectors options.

https://www.google.com/search?q=how+to+run+check+disk

afterwards, i would also do a disk defrag to complete the system tune up process.

incidentally, the check disk can be executed via the windows desktop or via a windows bootable cd

there are times when the file system is too corrupted, that running check disk via the windows explorer is futile and so the only option is to boot the computer with a windows cd.