For the last couple of days explorer.exe has been closing and starting every 5-10 seconds with no warning or error message. I can actually see it disappear from the task manager. When that happens, the entire desktop disappears including the task bar. Sometimes it comes back in a few seconds and repeats again and again. Other times I have to do File - New Task and C:\windows\explorer.exe from the task manager. Then I only get it back for a few seconds. Needless to say I can't do much in the few seconds its open for. I tried running every anti-virus scan in my arsenal, nothing worked. It happens in SAFE Mode too. Thinking there was something wrong with my explorer.exe file (dated 8/18/2001), I replaced it with a copy of the explorer.exe file from my wife's computer (dated 6/13/2007). Once I did that, everything was stable. However, the only way that works is if I do an "end task" on the old explorer.exe, then open a command prompt and copy the new one over the old one and RUN explorer.exe again. But once I reboot, it reverts to the 2001 version of explorer.exe and i'm back at square one. How can I prevent my machine from reverting back to the bad explorer.exe?

First thing is, it might not be explorer.exe itself that is corrupted. It could be one of the DLL files that the newer version uses that the older one doesn't.

You could try 'System File Checker'.
http://www.updatexp.com/scannow-sfc...

If that doesn't help, maybe a 'Repair' install might be called for.
http://www.microsoft.com/windowsxp/...

Yeah I was just going to suggest a repair install

You say ---
I tried running every anti-virus scan in my arsenal, nothing worked.

Do you check for, and remove, Spyware ??
Spyware includes ----
Adware, Dialers, Browser Hijackers, Trojans, Cookies,
Key Loggers, Trackware, and other Malware while browsing the internet.

Most Virus and Spyware scans are likely to work better in Windows Safe-Mode.

Yes, I meant I checked for all of that;malware, spyware, virus, trojans etc. I ran Spybot, Ad-Aware, Spyware Doctor, Registry Cleaner, Super-Anti-Virus, Trend Micro online scan. You name it. In safe mode too. Still the same problem.

The repair install of XP didn't work either.

What else can I try? Any ideas?