If I were you, I would check for system event log ; you may have a problem with the hard drive hosting your C: partition.
If there are errors reported in there, you should check for the health of this drive from a command line:
chkdsk c: /r
and answer yes when it asks you whether you want to do it at next reboot. Then reboot and wait for the end of the process (which may take a long time if this partition is large and you have a lot of files in it).
If there are no errors with the partition, then I would try to backup the database, dropt it, and restore it back from the backup.
Hope this helps.