Windows 7 updates failing with error code 800736B3

Hi, after successfully installing windows 7 (my first windows install since XP, after which I moved to Ubuntu) and doing the initial set-up etc., installing my own anti virus software and MS Office etc, I thought it was time to let it update itself.

however, every time I tell it to update then shut down it fails. I tried to troubleshoot it using the MS help box which was very little actual help, and then tried to initiate the update manually, however, when it comes to installing some windows 7 security and system updates and some IE updates, installation fails, resulting in error code 800736B3, whatever that means. The updates it fails on are:

security update for INternet explorer 8 for windows 7 (KB974455)
security update for windows 7 (KB974571)
security update for windows 7 (KB975467)
update for internet explorer 8 compatability view list for windows 7 (KB975364)
update for internet explorer 8 for windows 7 (KB976749)
update for windows 7 (KB974431)
I'm currently running avast! (v4.8 home edition) following Windows 7 informing me that it would not allow AVG to run (it was from an 'untrusted source' apparently, despite having been working a few days previously), but thats another problem entirely

Any help than can be offered will be much obliged! All I've been able to turn up from googling is a command that un-registers windows, which then for some reason allows the updates to occur, following which I can use my original activation code (given to me by digital river with the student upgrade deal) to re-activate windows, although I am reluctant to try this!

Many thanks

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