If you have a general crash problem with that PC, but Norton Diagnostics didn't find anything, it could either be a tricky, hard to find hardware fault - like a damaged capacitor on the mainboard - or some software running amok.

To test the latter, change the WED Video drivers in Preferences/Video Out to GXLBASE.DLL (the windows won't look right but you can ignore this for the test), and then start Windows in safe mode. This eliminates most drivers and programs running in the background. Now try to build that level in safe mode and check if it still hangs.