Try this fast test. Remove the case cover, point fan at open case.
Dell Dimension DIM 3000
Intel (R) Celeron (R) CPU 2.66 GHz, 2.00 GB Ram
Microsoft Windows XP Home, Version 2002,Service Pack 2
Dell Photo A10 Printer 962
Dell 2-button USB optical mouse,DIM
Cursor hangs, get 2 descending musical tones followed by 2 ascending tones, cursor frees...over and over again.
A-Squared found and removed Worm.Win32.Trafaret.a but this didn't solve the problem.
I would appreciate any suggestions on how to proceed.