The f****ing internet start page

hi guys, its been a while since i last wrote sorry bout that dont really have the time.
so heres the problem: i have as start page www.google.com, but since like a week or so, sometimes the the start page changes alone to another wierd search engine page. i've hijackthis and it appears sometimes then i delete them, but they keep appearing. i've also run norton and spybot and adware, but nothing.
any help welcome, thanks
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Wow, it would seem that between HijacKThis, AdAware, Norton and Spybot that they would find something. Can you provide anything else?