Mac Pro crashes everything constantly

I have a 1,1 Mac Pro running 10.7.3 . Has 11 GB of RAM and a ATI Radeon HD 5770 two 1.5TB hard drives and two 55GB hard drives. Everything else is factory.

The past few weeks it has been acting weird for the first time ever.

I first noticed that it would no longer launch Aperture because it said the grahpics card did not meet minimum requirements.

In iTunes, it won't show videos (just blank screen) or album artwork.

It won't load any kind of installer app.

It won't load system preferences.

It won't load the console.

It will load the terminal.

Won't load Safari. Will load Mail.

The computer itself seems to be running at around half the normal 'speedyness'.

I've tried downloading the OS X install update to 10.7.3 to install, but the install crashes. I've tried downloading the safari update and it crashes. I tried downloading Lion again through app store and it crashes when I get to the password screen. Every option I have to try and get my computer back up.... it crashes.

I have no idea what is going on. But I am in graduate school online and I can't afford to spend 3 hours a night trying to fix this thing!