CRYSIS WARHEAD issues.

Hey Guys, I kind of need some advice here. I recently bought a brand new computer (about a month ago). It's a Dell XPS 420 with an Intel Quad-Core running at 2.45ghz, 3 gigs of RAM, and a GeForce 8800GT at 512mb. I played and beat Crysis twiceover on near max settings, but max settings produce a pretty terrible frame rate. So anyway. I bought CRYSIS WARHEAD just the other day, and I made it about halfway through the campaign when things got bad. Now if barely plays single player on any settings, when I try to load my savegame it blacks out before it loads and says the graphics drivers malfunctioned, and now the original Crysis plays terribly also. What could cause such an immediate and dramatic difference in power? Not even Crysis Wars plays smoothly anymore. I tried to download new drivers but they were up to date.
Anyway. Any help would be greatly appreciated.

Cause I mean, I checked my computer's rating and it gave a 5.5, Crysis Warhead says it only needs a 5, 3 minimum. What's wrong? Shouldn't my PC be able to breeze right through this?

well I just got crysis warhead and I think they REALLY did do a good job on the visuals and optimization this time...I can play warhead with everything on Gamer (havent tried Enthusiast yet...too intimidated...) at 1920x1080 on my 24" monitor and it plays pretty smoothly (dont know exact fps though...need to find out/remember what command shows me the fps...wish they had a setting that always showed u the fps, rather than each time typing in the command...like net_graph 3 from half life and company )

Thanks for the help. I re-installed the game and the drivers, it seems to work a little better now. This is a little off topic, but my windows takes 3 times longer to start up all of a sudden. What could cause that? I mean, other than a lot of programs running. I'm not sure if I do. I checked, there isn't too many.

So I re-installed the game, then re installed the drivers too. I did a system defrag, spyware check, and a virus scan. I also cleaned up my software options on startup and turned off windows desktop manager. My computer takes about a full 30 seconds to load windows now and I can't play Crysis for one minute before textures pop out, the game lags, and then black squares and sky-colored bars dance on the screen. What could be causing this? Is it my video card? Has it cooked?