Keyboard wont work. Boots in Diagnostic Boot. Please help

I have been dealing with this problem trying to fix it for some time. I have a Dell inspirion 600 PP12L running windows XP home edition. my service tag is <ADMIN NOTE:Service tag removed per privacy policy>

What happens is if i turn on my computer it will turn on and say "Diagnostic Boot Selected" in the top right corner. If i let it go through it will stall once it gets to multiple colored bars asking if i see lines pres y/n. My keyboard is unresponsive so i cant select anything or hit ESC to exit the diagnostic boot. However if i turn on the computer while holding ANY key it will start right up. It beeps a few times but continues booting as normal. Once the computer is to the desktop and i go to use the internet or something the keyboard wont work at all. NO keys work.

I have replaced the keyboard with a brand new one.

I have reinstalled windows on the computer.

I have reseated both the hard drive and keyboard multiple times.

I have tried uninstalling the keyboard driver and reinstalling a new one but that dos'nt work.

I dont have any other problem with the computer. i can use the mouse pads and buttons and the on screen keyboard.

I would really like to fix this issue because the computer is fine other then this problem. If anyone could offer some help/advice it would be greatly appreciated