PC can't install Windows updates

[mauve]

Got myself a new PC, Alienware X51 R2. It's running Windows 7, and it's been working great so far, but it has a problem downloading Windows updates. Every time I boot it up, it tries to install updates, then at about 35% it says "Updates failed. Reverting changes."

Dell no longer provides email or live chat support for this model (Yay I bought it three months ago. Good to see it's obsolete.) and phone support won't do anything unless I give them permission to remotely access my PC. I hate doing that, so I declined.

My only other option is to take this in to Best Buy or something, which is fine, but considering I've had bad experiences with them ("Ah, your graphics card is fine. We used your PC to play Left 4 Dead and nothing happened." Two days later graphics card is shot and I basically paid them to play my video games without my permission.) I thought I'd ask you folks for advice first. Any hints as to what might be going on and how to fix it? I've had problems with my antivirus software messing with Steam downloads, but I doubt it would object to things that actually come from Windows. But then, I might be wrong.