system running slowly

Hi there, sorry to trouble you...

I'm a bit worried about windows, it works fine for most things but is sometimes acting strangely and some programs will barely run at all (farmville, yahoo chess and my professional email account). Sometimes things don't log in even though I've put in the right password and I frequently get an error message when loading a webpage. malwarebytes, avgfree and spybot all found nothing but I'm worried i might have a rootkit worm. Would it be possible to post a hijackthis and combofix log on here please?

Many thanks
Matt