IE home page changed

I m using wimp with 2 users a/c both r administrator & facing problem in one a/c. my Internet Explorer home page changed to

http://4-counter.com/?b=alexxp

I tried my best to change it 2 Yahoo & it restore it on that time but when I restarted my system it comes to the above address again. Even I used Ad-aware v6.0 Personal build 6.181 & SpyBot – Search & Destroy v1.2 to delete any ad-aware or spay ware and it found 600 entries & I
deleted all that with the hope that it might work. But nothing happened. I searched my system & registry and deleted all entries containing above name and when I restarted the system it come again.

Pls tell me how can I changed my IE home page it Yahoo permanently.