Finally i seem to have made sense of it all!
After looking through various threads and issues on the internet i somehow stumbled across a problem somebody had with GTA4 and a patch for Games For Windows Live.
I gave the patch a quick go, but still had no luck.
However, this evening i took this a little further…
I run Windows 7 Professional, and by default on install the Games are not included, probably to stop you arsing about at work playing cards etc..
Anyway, i never bothered to install them as i never use them, but one thing it does loose is the Windows Game Centre application.
So, in Programs and Features, under “Turn Windows features on or off” i enabled the “Games” checkbox and let it do its thing.
Removed the MP3 install (again), cleaned the registry (again), rebooted and reinstalled.
Once again the whole thing ran through fine and started up at the end… but this time…
The Social Club sign in appears!
And i can finally bung my activation code in!
And with that accepted the intro video began!
And then i had to bug it out, as its now 00:15 and i need to be up at 05:00 - damn it! Should be home for a couple of hours after so can give it some proper play for the first time!
One of the previous posts about updating the Social Club is completely useless… apparently that isn't even supported any more? God knows why that was suggested!
Anyway, happy now!