Windows 7: Windows 7 fails to install - upgrade over Vista

I think 've tried everything. Upgrade advisor says all is fine, all drivers report as updated, no camera etc connected, virus scanner removed, possiblely tricky software removed etc. PC meets specs. I specify upgrade, it goes through all the motions right through to the final steps of installing apps etc then part way through (and i cant say when) it restarts back to Vista, with a message that it was not possible to install. No error message that I have seen.

I suspect I need to try a clean install but before I do...any ideas welcome.

Intel QuadCore 2.4, 4MG RAM; GF2400 GT, tons of disk space

Welcome Dodgie, Have a look here,
Doing a Clean Install with a Upgrade Windows 7 Version

Check the last listing in install logs for clues for what caused the failure:

C:\$WINDOWS.~BT\Sources\Panther\setuperr.log
C:\$WINDOWS.~BT\Sources\Panther\setupact.log
C:\$WINDOWS.~BT\Sources\Panther\miglog.xml
C:\$WINDOWS.~BT\Sources\Panther\setupapi\setupapi.dev.log
C:\$WINDOWS.~BT\Sources\Panther\setupapi\setupapi.app.log
C:\$WINDOWS.~BT\Sources\Panther\PreGatherPnPList.log
C:\$WINDOWS.~BT\Sources\Panther\PostGatherPnPList.log

Try clean booting Vista to run the Upgrade:

type msconfig in the Start Search box, and then press ENTER.
In the System Configuration Utility dialog box, click Selective Startup on the General tab.

1. Click to clear the Load Startup Items check box. Note The Use Original Boot.ini check box is unavailable.
2. Click the Services tab.
3. Click to select the Hide All Microsoft Services check box.
4. Click Disable All, and then click OK.
5. When you are prompted, click Restart.

Clean Install Windows 7

With or without problems a clean install is always bet. Not too much extra work now. You just have to reinstall programs.

But you save a lot of time and effort later.

Do a clean installation, now. You will save time by not trying to solve this problem.