1. ESET Online scanner:
http://www.eset.com/onlinescan/
2. Housecall:
http://www.trendsecure.com/security_solutions/housecall_free_scan.php
The above scanners will try remove what it detected as malware, virus, worm or trojans etc.
If removal failed, please download HijackThis then post your log in HijackThis forum. Please read the instruction at:
http://forums.cnet.com/5208-6132_102-0.html?forumID=32&threadID=255339&messageID=2533167

To identify the malware and if the above online scanners did not identify anything on your PC, use the online scanners below:
NOTE: This scanners below DO NOT remove what it finds. You will need to download trial of Kaspersky antivirus to remove the trojan or download the a-squared program from http://www.emsisoft.com
1. Kaspersky online scanner:
http://www.kaspersky.com/virusscanner
2. TrojanScan:
http://www.windowsecurity.com/trojanscan/
3. Or use PrevXCSI Free (no installation required to detect only for malware). Download it from http://free.prevx.com/
When these scanners detected it, please tell us the risk/threat name.