Mac pro 2,1 boots up but won't restart?
-What happens if you take the memory out and replace it with the original RAM?  Does it work?  

-Have you tried re-seating the RAM? (e.g. take it out and put it in again, making sure it's fitting in the slots properly, and also making sure there's no dust on the RAM or in the slots...)

-Is the RAM PC5300 DDR2 ECC?

-Have you tried resetting the SMU?  http://support.apple.com/kb/HT3964?viewlocale=en_US&amp;locale=en_US

Give those things a go and see what happens.