Some general things to try.
See if System Restore will get you back to a restore point before your problem with Explorer, OR try the System File Checker.
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista (or 7)
http://support.microsoft.com/kb/936212/#appliesto
How to analyze the log file entries that the Microsoft Windows Resource Checker (SFC.exe) program generates in Windows Vista
http://support.microsoft.com/kb/928228#appliesto
How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7
http://support.microsoft.com/kb/929833
Try Safe Mode (Do you have this problem in Safe Mode?).
Advanced startup options (including safe mode)
http://windows.microsoft.com/en-US/windows7/Advanced-startup-options-including-safe-mode
If you cannot reproduce the errors in Safe Mode see if you can further isolate the cause.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/default.aspx/kb/929135
Try running ChkDsk to check your drive for errors. Right-click your Drive icon/ Properties/ Tools/ Error Checking. Try it first by not checking either box (Read-only mode) to see if it flags any hard drive or file problems. If it does, start by ticking both boxes, in any further rerun.
Create another user and see if they have the same problem as your current user.