Have you tried starting your computer in Safe Mode? If it works correctly in Safe Mode, try uninstalling, then reinstalling the new antivirus software.
By the way, did you uninstall the McAfee software before installing the AVG? If not, in Safe Mode, uninstall the McAfee and then the AVG, then reinstall the AVG.
I hope this will help!
Dwight
P.S. How to start the computer in Safe Mode
"For all versions of Windows, repeatedly tap F8 after the self-test beep to invoke the Boot Menu, then choose Start Windows in Safe Mode.
For Windows 95 through ME, you can substitute F5 to go directly to Safe Mode, bypassing the Boot Menu.
For Windows 98 and ME, you can press and hold Shift to start in Safe Mode, or Control to invoke the Boot Menu."
TomGL2Copy/pasted from
TomGL2's post
here.