Sorry for the delay in replying to this. You may need to remove and reinstall AVG.
Scan with hijackthis and have it fix the following entries:
O3 - Toolbar: (no name) - {E0E899AB-F487-11D5-8D29-0050BA6940E3} - (no file)
O4 - HKLM\..\Run: [NvMediaCenter] RUNDLL32.EXE C:\WINDOWS\system32\NvMcTray.dll,NvTaskbarInit
Close any open windows, other then hijackthis, before hitting Fix checked.
Go to C:\WINDOWS\system32 and delete NvMcTray.dll
Empty your Recycle Bin, reboot, close any open browser windows, scan with hijackthis, and post a new log. Also, describe any problems you are still having, please.