Before trying out System Restore, it's better to a disk check. When you boot into Safe Mode, open a Command Prompt window and type the following command:
Chkdsk will most probably say that the disk is locked and will ask whether you want to schedule a disk check on next bootup. Type "Y" or "Yes" to allow it. Next, reboot the PC and allow chkdsk to run. Once the disk check completes, try logging in in normal mode...