It is very likely to be caused by virus. Thus, I would like you to go for a online scan first and then see if it fix anything.
Please go HERE
to run Panda's ActiveScan
- Once you are on the Panda site click the Scan your PC button
- A new window will open...click the Check Now button
- Enter your Country
- Enter your State/Province
- Enter your e-mail address and click send
- Select either Home User or Company
- Click the big Scan Now button
- If it wants to install an ActiveX component allow it
- It will start downloading the files it requires for the scan (Note: It may take a couple of minutes)
- When download is complete, click on My Computer to start the scan
- When the scan completes, if anything malicious is detected, click the See Report button, then Save Report and save it to a convenient location.
After which, follow this set of instruction
and post try to post your HijackThis log here
Remember to post the contents of the ActiveScan report together with the HijackThis log in HijackThis Logs and Analysis Forum.