Ad-aware is another good one to run on your computer , an' try the free AVG too.
<a class="postlink" href="http://www.lavasoft.com/products/ad_aware_free.php" onclick="window.open(this.href);return false;">http://www.lavasoft.com/products/ad_aware_free.php</a>
<a class="postlink" href="http://free.avg.com/download?prd=afe" onclick="window.open(this.href);return false;">http://free.avg.com/download?prd=afe</a>
i know some of the better ones are a bit costly but look closely at their sites .... sometimes they'll offer a full working version of their product on a monthly trial basis (a try before you buy!) ..... just download it , use it until the trial expires , then get rid of it ..... unless , of course , you like it that much that you fancy payin' for it.
Think Trojanhunter , for one , offer such a trial ....
<a class="postlink" href="http://www.misec.net/products/TrojanHunterSetup.exe" onclick="window.open(this.href);return false;">http://www.misec.net/products/TrojanHunterSetup.exe</a>
If it's really in a right old state ...... download 'hijack this' , run it , and post the log it presents you with onto one of those computer geeks sites ..... they'll be able to tell you what's wrong with it!