Did you download the latest version of AVG ?
I would suggest to first download AVG FREE from here and put it on your desktop:
Pls. scan the AVG download after downloading with your AV.
Then I would suggest to UNINSTALL the version of AVG you have on your computer with the AVG Remover.
You can find it here:
reboot your computer and install the AVG version you just downloaded.
I download the Free AVG and ti works fine, but when I turn my computer off for the night and then turn it back on in the morning, it comes up with a certificate saying there is an error, and it offers to re install but when I try the folder it wants cannot be found.