Following is a workaround for Vista/Win 7. This defeats the security feature that calls for the scan so all downloads should be manually scanned before using.
Copy the lines between the stars (but not the stars):
Windows Registry Editor Version 5.00
Open notepad and paste the above into it. Verify that you have it all then File, Save As, (to your desktop) "NoScan.reg" OK (Make sure you includes the quotes around the file name)
Close notepad. Right click on NoScan.reg and select Merge. Allow it to merge. (If you don't see the Merge option you probably left off the quotes and notepad tacked on .txt)
What I think is happening is that AVG (or some other anti-virus tho AVG seems to be the most common) attempts to stop Windows Defender and take its place in the scan but somehow breaks Windows Defender. No proof yet.
Sometimes this doesn't fix IE but will fix your other browsers like Firefox or Chrome. I have had to uninstall IE and let it revert back to an older version a few times. Some people claim that removing Windows Defender and deleting the folder C:\Program Files\Windows Defender or C:\Program Files (x86)\Windows Defender will also fix it.
If you have Firefox then you can fix it without a registry edit. Open Firefox, Type about:config in the URL box and hit Enter. Scroll down to
and double click on it. That will change the Value to False. Close Firefox and restart. It should allow you to download files now.
I've also seen the same symptom with a Zero Access infection so if the above doesn't work that may be what you have. I would need an OTL, Quickscan log to tell. Download OTL from
and Save it to the desktop of a friend's PC then copy otl.exe to a USB drive and then move it to the desktop of the sick PC..
Run OTL (Vista or Win 7 => right click and Run As Administrator)
Click on Quickscan. When it finishes you will get one or two logs. Copy and paste the OTL log.