Desktop Icons Move Around

Two fresh installs of W2000 and everyday my icon on my desktop will shift aorund and some will disappear until I refresh (F5). Then I have to arrange them all back in sorted order by name.
I use Tweak UI but it does not help. No weird programs other than Norton SystemWorks, Office and basic stuff.
People have said it is a virus… please!!!!! I know viruses and this is not the cause, and there are none on my machine.
What can the cause be?

W2000 Pro
SP 2
500MGZ
300+RAM