Hello aussiestyle,

could you please describe the situation in more details?
Is there any error message or BSOD (Blue Screen Of Death) before the automatic restart?
Is possible to boot into Windows Safe Mode? Then try to uninstall AVG and check the situation again. Check also folder C:\Windows\minidump for any recent files, pack them in an archive and upload it to some online storage (then provide us with link to that archive).
Which AVG version are you using? (AVG 2011, 9.0, 8.5)
Which operating systems are affected?

We are not aware about any similar reports right now.

Thank you