First download, install, update and run SpyBot Search & Destroy from the following site:

http://security.kolla.de/

Let Spybot get rid of any parasites it finds.  If this doesn't solve the problem, do a search on your computer for the file named hosts (note that it has no extension and is not the file named hosts.sam).  When search for this file make sure that you include system files and hidden files in your search.  When you find the hosts file, rename it to hosts.old.  Reboot and see if this solves the problem.

Steve

If steve's advice does not help try this:-

Use these to remove Malware (Spyware and Adware).
Spybot S&D
Ad-Aware
Cwshredder
With all of these download them, install (after unzip if required), download the latest signature file, run, delete all that they find.

Failing those solving your problems a post of a hijackthis log for the experts to advise.
HijackThis From Here
Download, run, scan, save log, then in notepad copy the FULL log by copy and paste to a post in one of these specialist spyware removal forums:-
http://tomcoyote.org/forums/index.php
http://forums.spywareinfo.com/index.php
http://www.net-integration.net/cgi-bin/forum/ikonboard.cgi
http://boards.cexx.org/index.php
DO NOT FIX ANYTHING WITH HIJACKTHIS WITHOUT EXPERT ADVICE, most of what it finds you need for normal MS Windows tasks.
Do read the sites FAQ before posting, and advise your problem and what steps you have already done to try to cure your problem.

I am in all those sites as ChrisRLG. You might get me, but any of the more problematic ones are handled by the experts. If you get a 'advanced member' like me, we have other ways of asking for advice from the experts, to pass on to you.

You could post your log here in this thread (if in the Virus Information and Removal Board - if not post in that board not in this thread), and I will have a go at giving advice, but if you go to one of the more specalist forums more experts will be able to help.