May be a hardware problem.
Make sure you have all the DRIVERS up to date from the manufacturer for your EXACT model of laptop AND version of Windows.
You could also try burning a bootable copy of Ubuntu to see if your keypad works in it (in which case it's a Windows software issue).
To boot from CD/DVD you need to change the BOOT order in the BIOS (such as: 1. CD, 2. hard drive)