I just bought the EXACT same Dell. Been having issues with gaming. After twenty minutes or so into SupCom, Neverwinter Nights 2, Crysis, it will crash out to windows. Windows itself operates normally. No issues with physical memory.
Drivers for the Radeon?
Also, this case runs hot when the video card has a demand on it, but for whatever reason, Riva Tuner doesn't want to display temps. TheXPS Studio is a mini tower in all respects and has only two openings that will allow any kind of ventilation. Could cook an egg on top of the thing sometimes. ]:\