The computer is stopping at the POST test screen because the computer has had a hardware fsilure or a virus has destroyed the MBR. You will need to use a XP CD to find out where the problem is. If windows will not load from the XP CD you probably have a bad hard drive, CDrom drive, motherboard, or memory. What happens when you keep hitting the F8 key while the computer is booting up. Does it get into the blue screened BIOS screen. If so, does it show the hard drive in the BIOS?No HD in the BIOS says its dead. If you can't even get into the BIOS the motherboard is suspect, but first try some different memory that is compatible. Also set the BIOS boot order to firsat boot from the cdrom drive. Then you can try a XP CD and see if it will load up.
XP will ask you if you want to setup windows if it will boot from the CD. For right now you will say no and just shut off the computer. What we are trying to do is find the hardware problem first.