Windows XP Virus problem

In Some windows XP PCs i am facing a problem that, when i open My Computer,explorer, control panel it will not open . instead of that all desktop icons will diappear for two sec and will come back. Since it is affected in more than one PCs i think it is a virus. But i have Norton 2003 with latest virus defenitions which is not identifying any virus.Now what i am doing is formatting and reinstalling.
i tried removing all startup items and all that.
Also there is no new programs or hardware installed recently.
But in safe mode windows will work properly.

Anybody has an easy solution to this…? pls reply