I solved my problem by downloading free software from the internet. -CWShredder- My home page kept switching to "Cool Web Search" and no matter how many times I changed it back to "My Yahoo", it kept changing back. Maybe it will help your problem also. here's a link....
http://www.spychecker.com/program/cwshredder.html
I found another guy that had the same problem on another board and he told me about that site. I think I am still going to reload my OS soon, but at least my girlfriend can check her mail now.
Good luck !