Runs but wont move

that is a good car so I would let a shop do a Diag correctly

Sounds like your throttle cable has came off or broken. Have someone sit in the drivers seat and press the accelerator repeatedly (with engine off) while you look in the engine compartment for movement. if nothing moves your cable is broken and you will need a new one. as for not starting, the cable could be binding the throttle body, but that's only if the engine cranks over. if the engine wont even turn over, you may have a bad alternator. Worst case scenario though is that you have broken your timing belt and basically scrapped the motor. I would highly recommend a tow to a mechanic. Hope this helps

sounds like you speed sensor and your throttle poistion sensor

Sound like low engine compression
head gasket gone between the cyl

Sounds like a basic miss or fuel problem.
Have you had the computer scanned for trouble codes ?

If the check engine light is not on, it could be low fuel pressure and/or a dirty fuel filter.
On this model the fuel filter is in the gas tank.

Sounds like you need a new shop.. AND A LAWYER!!!

sounds like you have moisture in the gas tank. there's plenty on the market that will take moisture out of gas tanks. Home Depot, Menards, etc.

Kdog

change your clush plate or gear if its in place

Check out this recall:

http://www.automotive.com/2004/49/pontiac/grand-prix/recalls/45415.html

Springs or the cable might be a problem. Check on the recall and then go from there.