when i choose windows XP it goes directly to the XP home screen with the green bar at the bottom

MemTest
--------------------------------------------------
Try running MemTest.

i ran XP and tapped F8 like no other...still nothing.

Run MemTest or boot into Vista.

If you can boot Vista the RAM is probably ok.

If not then run MemTest as it is probably not ok.

well i cannot open vista either i dont even know what happens

Run MemTest or try new RAM.