Ok, so i just finished building my new pc; i insert the xp disc, i see the blue screen that partitions my hard drive (which took forever) and my computer restarts, like normal. I see the xp loading screen, and then i see the setup screen. A few seconds later, my pc just shuts down without warning. Whats wrong?
 
specs:
q9300
evga 780i  
9600gt
wd5000aaks hdd
gskill 4 gig ddr2 800mhz
 

If windows restarts or bsods out of the blue, it may be memory. Run this for 5+ passes:
 
http://www.memtest.org/#downiso
 
If it fails, up the vdimm to 2.1v in bios.

If you are trying to overclock anything, put all settings back to default.  Once you have a stable system, then start playing.

Well, i ran memtest v2.01 and everything checked out. I took out the hard drive from my old computer with xp and plugged it into my new one, and the computer managed to boot; I could see my accounts and such and when i tried to access my account, it required an activation, either by phone or internet.

What XP disk are you trying to install from?  Is it a full version or a recovery disk that came with a store bought computer?

Disable graphic boot screen in bios if possible.
 
When the pc posts, is there is message at the end of the screen that reads "Verifying DMI Pool Data..."?
 
If so, does it say "Update Success"?
 
If not, you may have a problem. You have to shut down, unplug power cord, clear cmos, wait a min, then hook things up. It MUST update success.

Yeah, it didnt say "update success", thx akhilles, and ur method works!!!!