ASRock 939 mobo system not booting into XP

I'm building a system and its not booting into Windows XP.

Here are the specs:
-ASRock 929 dual SATA board
-Antec 400W PSU
-Athlon 64 3200 Venice cpu
-6600 GT (128mb)
-Corsair Value Select 1GB (2x512mb) DDR400 RAM

What happens is its posting and getting to process of starting Windows and it restarts.

I suspected RAM at first, so I:
-Removed 1 stick
-Placed that stick of RAM in several slots, trying to boot each time
-Tried my backup Kingston value ram (DDR400) the same way, no luck

I tried booting into safe mode and it restarts when agp440.sys loading (I have selected PCIexpress in the BIOS).

The hard drive I'm using was in a different system and still has XP on it. Is it possible I need to reinstall XP to get the system to boot? Any other ideas?

Yes, you must reformat and reinstall Windows when you switch motherboards. Even if you were to get it to boot it would remain unstable.

rseven is right, you have to repair or reformat/reinstall windows whenever you change chipsets