Crunchie will probably have some other ideas, but until he gets back to this, try these suggestions:

Get SilentRunners from here:
http://www.silentrunners.org/

Run it, and save the log that it generates.

Get the Pocket Killbox from here:
http://bleepingcomputer.com/files/spyware/KillBox.zip

Unzip the file to your desktop.

Boot into Safe Mode and do a search for these files and delete any instances found (be sure your system is set to Show hidden files and folders):

param32.dll
guninst.exe
popup_bl.dll
systr.dll
svrhost.exe

If you find any of these files, and any could not be deleted, run Pocket Killbox and paste the full file path of file in the box and click on Delete on Reboot. Click on the button with the red circle and an X in the middle; you will get a message saying File will be deleted on next reboot, Process and Reboot now?, Click Yes to reboot. (Note: the 'file path' will be something like C:\WINDOWS\System32\param32.dll)

Reboot normally and delete any icons from your desktop that you did not put there..

Empty your Recycle Bin.

Close any open browser windows, scan with HJT, and post a new log along with the SilentRunners log.