Can't get past splash screen on old Compaq

Ok I have an old Compaq computer with 256 megs of RAM, Pentium 4 processor and 80 Gig IDE HDD. I have no use for an old computer with old technology but I was going to donate it to a local school. I pretty much took everything apart and stipped it to the bare bones. I dusted and cleaned everything. So after that I put everything back together and booted up the computer. Everything booted fine and a fresh copy of WindowsXP was re-installed without any problems. I installed all the drivers from HP's website and re-booted. After re-booting it said "boot device not detected insert boot media. So I thought ok maybe something was disabled in the BIOS I'll just re-boot and do a quick check. Thats what I did and once the computer got to the Compq splash screen it froze there. I re-booted again and tried it again, again it froze. Now I can't get past the splaah screen. Any idea's of what is causing this problem and how to fix it? I don't see how it can boot up, install Windows and install the drivers then just not boot anymore.