Install avast antivirus, download the update, and then, when it asks you if you'd like to do a boot time scan, say YES, then restart your computer, when your computer boots, but before windows starts, the antivirus will scan your computer and delete any viruses, trojans, or malware before it has a chance to launch with Windows.
http://avast.com/eng/download-avast-home.html (excellent antivirus and free for home use)
I also recommend you download a copy of Trojan guarder, get the update for that, and run a full scan with it.
http://download.cnet.com/Trojan-Guarder-Gold/3000-2239_4-10165573.html?tag=mncol
(Trial software, us it for free until the trial runs out, then buy or uninstall)
After your computer is clean, download all the Windows security patches, make sure the Windows firewall is on, and then go get a small physical firewall to go between your computer and the internet, linksys makes lots of inexpensive ones.
I'm an IT Administrator, so I know what I'm talking about. This is good stuff.