R13
The other asshole
If it's a prebuilt pop the side panel off and post some pics of it and any specs (CPU & GPU mostly) you know, That will help me know what can be done with it, i think you can make a decent upgrade with $600-800, That's close to what I'd need if I wanted to switch my budget rig over to a i7/Sabertooth setup so that should be plenty to work with for what you described.