You need to either/both
1) backup your system partition (for safety) to "free disk space" (on another drive, obviously....)
2) Run PartitionMagic's Partition check on EACH partition on that drive:
- Start PM, select a partiton on the target disk (start at left and go right-to-left doing each....), then select "Partition" -> "Check for Errors..." and the internal integrity checker will scan the disk for errors. (When/if you check the System partition it may require an auto-reboot....)
The backup is up to you, but run the check over until it reports no errors, then try using it on your system again....