Problem with explorer.exe in Windows XP.

Hey guys. I’ve come looking for help. I have a desktop running Windows XP and starting recently, everytime I start up the computer explorer.exe will not run. I’ve tried starting it manually and it shows in the process list for two seconds then disappears. I’ve heard sometimes Norton can cause things like this so in msconfig I disabled everything but the most important for startup and it still won’t run. Any help would be much appreciated.