Ok I ordered a new mobo and processor and received it yesterday.

AMD 4850e
GA-MA78GM-S2H

My old system is:
ASRock 775Dual-880Pro
Pentium D805
GeForce 7900GS
Corsair XMS 2x1GB DDR2 667
WD 250gb SATAII
Generic PSU that came with case (OKIA 500W)

So I installed my new mobo and processor (rest of the system stayed the same) but it won't boot.
The first time I turned it on, it posted fine but then froze while detecting hard drive. 2nd time it froze right after the post.
I tried a few more times but it just kept freezing. I removed one of the memory modules and it didn't freeze BUT it restarted itself before 1 winxp loading bar went across the screen. I planned on using Linux for this so I tried booting off that CD but it froze at the beginning of installation. I also tried going into the BIOS and I was able to go in there just fine and browse through the options, but as soon as it tries to load the OS, it restarts. I can't figure out why.

Everytime I restarted, system went through the POST just fine. 1 beep every time.
I tried other memory slots but only 1 seems to be at least getting to winxp loading screen (4 slots on board)

I took the processor and mobo out and replaced them with the old hardware, everything is working fine right now, that's how I'm able to make this post. I ran CPU-Z and it recognizes both of my memory modules so I'm thinking those are OK.

My questions:
1) what's wrong (obviously)
2) could the memory speed ratings be causing any of this? the new mobo has a DDR2 1066 standard and I'm using 667.
3) I noticed on my 4 pin CPU power plug...there's 2 yellow and 2 black, but 1 of the black wires is cut so there's really only 2 yellow and 1 black, i don't know if that matters but like i said old system is still running fine.
4) The problem is obviously either the new processor or mobo, right? but to me the processor seems fine...

Thanks for reading all of this and hopefully someone can help.

oh...well yea i knew I couldn't use the same windows for the new motherboard, thats why I had the linux install CD. I was going to install that on the hard drive but it freezes at beginning of install. Should I format my hard drive then try the new mobo and processor? (how?) I don't really want to do that because if the same problem happens, I don't have any computer....should I try booting from the software cd supplied with my motherboard?

Well I thought about that too, but its powering the old system just fine and I'm pretty sure the old system uses much more power. I had two 120mm case fans, 1 optical drive, the 7900GS and 1 floppy that I didn't connect on the new setup. Also, the new processor I think uses less power than the D805. The old mother board has a spot for the 4 pin CPU power connector also.

Edit: Motherboard manual says to install chipset drivers and other drivers after installing OS. Can't get installation of linux going though. I tested the CD on this old setup and it starts installing just fine.

UPDATE: I set the memory to 667 manually but it still didnt fix the problem. Then I bought 2x1gb ddr2 1066 corsair dominator. Computer booted with no problem using this memory. I don't know why but I guess the GA-MA78GM-S2H just doesn't like the corsair xms ddr2 675 series or maybe just mine. I'm just glad I got my system up n running.

oh btw, after getting the dominator i saw a deal on crucial ballistix ddr2800 2x1gb for 39.99 with 20 mail in rebate so it came out to 19.99! i picked up 4gigs of that and my system is working with that memory also.