Hi, welcome to the best Forum on the Net ... first thing to try is a System Restore back to before SP3 was attempted - Start>All programs>Accessories>System Tools>System restore, then choose a date shown in Bold print - before SP3!
After that, if still no good, run click here in its default form - in fact it would not hurt to run that anyway after doing the System Restore.
Any further problems, come back here - plenty of guys and gals ready and willing to lend a hand.
Also stick with this one Thread until completion, hopefully.
Finally, for the moment anyway, I would advise you to download the Forum Rules by clicking on the link at near the top of this page - the Rules are only a couple of pages.