First, try another keyboard. Does another keyboard work?? If so, then its probably a problem with the keyboard itself. If not, it is a software problem...
Is BIOS recognizing a keyboard on POST? If the keyboard can work at the DOS level before booting into Windows, then the basic computer sees the keyboard. In order to determine this, shut the computer down, re-boot with F-8 key held down. Do you get the DOS menu up??? Can you use the up and down arrows, and type at the DOS level? If not, then either the keyboard is not functional or is bad or BIOS is failing to recognize a keyboard...CHECK YOUR CONNECTIONS...is your keyboard securely plugged into the recepticle?
If the keyboard is working at the DOS level, but not in Windows, then you know the problem resides in Windows...not in the basic computer itself or in the keyboard itself.
You have to get into Control Panel-->System---->Device Manager and see if you have a keyboard driver installed there. See if you have a Standard 101/102 Key Keyboard Driver installed and it has no red X or yellow ? through the driver.
If the driver is Nixed with a red X or a yellow ?, you may need to do an Install New Hardware detect and let windows re-detect the keyboard.
If this is a specialized keyboard, you may have to have proprietary drivers for it...but I am betting a standard keyboard driver will work.
Its a tough work-around to get around windows without a keyboard...so I am hoping you will find out it is a hardware issue.