Mouse/XP problem

I run XP on an HP home computer.
I am experiencing a combination of three problems that are progressing beyond annoying:
1. When I click on a box with my mouse, the box often fills up with spaces involuntarily
2. When I move my mouse across a page, it often blocks off random segments of text without my asking for it.
3. The title bar and information within boxes on IE 7.0 often starts fluttering or rolling over and over through the list, again involuntarily.

I immediately suspected a virus, trojan horse, spyware. But I have completely swept my machine with three different programs and the problem still reoccurs.

Has someone experienced this same problem?
Did you find a solution?
Can you refer me to any website that addresses how to solve it?
Thank you
Noel