Sounds like the sasser virus.
This is the advice I followed when I had your symptoms, worked for me.....
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"Download the FxSasser.exe file from:
http://securityresponse.symantec.com/avcenter/FxSasser.exe
Note: Version 1.0.1 (As shown in the removal tool dialog title bar) provides
support for both W32.Sasser.B.Worm and W32.Sasser.Worm.
Save the file to a convenient location, such as your downloads folder or the
Windows desktop, or removable media known to be uninfected.
To check the authenticity of the digital signature, refer to the "Digital
signature" section later in this writeup.
Close all the running programs before running the tool.
If you are on a network or if you have a full-time connection to the
Internet, disconnect the computer from the network and the Internet.
If you are running Windows Me or XP, then disable System Restore. Refer to
the "System Restore option in Windows Me/XP" section later in this writeup
for further details.
Caution: If you are running Windows Me/XP, we strongly recommend that you do
not skip this step.
Do one of the following:
If you are running Windows NT/2000/XP, skip to step 8.
If you are running Windows 95/98/Me, restart the computer in Safe mode. For
instructions, read the document, "How to start the computer in Safe Mode."
Double-click the FxSasser.exe file to start the removal tool.
Click Start to begin the process, and then allow the tool to run.
Restart the computer.
Run the removal tool again to ensure that the system is clean.
If you are running Windows Me/XP, then re-enable System Restore.
Run LiveUpdate to make sure that you are using the most current virus
definitions."
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Good luck.
Nik.
