Hi and welcome to the Forum

This is quite a common problem and is usually due to a faulty installation of the USB Driver. It is very important that the driver installation procedure is followed exactly, if successful USB communication between keyboard and PC is to be achieved.

You can download the procedure for Windows XP from my website : http://www.willumspages.co.uk/page10.html - It's Tip number 1
I suggest that you remove your previous installation first.

If you are using an External USB Hub, this can sometimes cause communication problems. If this is the case, try connecting the keyboard directly to the PC.
Other thoughts : Try a different USB Port : Try a different USB cable or check that the cable is OK, by using it to connect another peripheral to the PC - printer, scanner etc.

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Willum