Installation of AVG8.0 failed; can't revert to AVG 7.5

I've been using AVG for years, and up to this morning was using 7.5 with all updates. Ironically I was making installation instructions for a PC novice who has no virus protection, for whom I'd downloaded the installation file, and was running it on my PC to be able to take screenshots so that he could follow the procedure. I realised that this was a new version, and thought I might as well complete the installation. Unfortunately it failed. It removed AVG 7.5 as part of the process but failed at the end with a registry error. Since then I've been thrashing about wildly to try to recover the situation
1. I removed AVG 8.0 andI searched for AVG 7.5 in the hope of reverting to 7.5. Couldn't find it
2. I restored to a restore point of yesterday. This recovered AVG 7.5 but it won't run. For example if I try to open Outlook, I get the messages "AVG kernel - Cannot create and instance of AVG 7 Kernel; err=0x80040154" and "Microsoft office outlook - The add-in "c:\progra~1\Grisoft\AVGFRE~1\avgxch32.dll" could not be installed or loaded.....use Detect and Repair". Detect and Repair fails.
3. I tried to delete 7.5 in the hope of installing an alternative temporarily but it refused to uninstall. I deleted all files from c:\programfiles\AVG and c:\programfiles\grisoft. I then ran System Mechanic which repaired some registry errors and tried to install again - same error.
I've E-mailed Grisoft but as it's the free version they might not help. I downloaded and tried to install their paid-for version, but that also fails to install.

Can anyone please suggest how to recover from this? Ultimately I could restore using an image but my last one is a few months old and I'd lose some work. I do have a backup of all my important user files though, made this morning, so it wouldn't be a disaster. However I'd rather fix it if I could.

Thanks

StuartStart Free Trial