Strange Keyboard Problem with Arrow Keys and Numlock

> Okay, basically, with Num lock on, the arrow keys and the
> 9 above them (excluding scroll lock and pause/break) do
> not respond correctly in some programs (register as
> SHIFT). With Numlock off, they register fine, BUT, in
> some programs they don't even register. So I wrote a
> quick program to see that the KeyUp and KeyDown events
> were returning to the system. With Numlock on, pressing
> i.e. Right arrow key led to the Keydown event flickering
> from 'None' to 'Right' and the Keyup event returned a
> flickering from 'Right' to 'None'. On a friends "normal"
> computer, each event correctly responded with 'Right'. I
> noticed this problem at the end of May(!). So I tried to
> revert my system to as it was before that (BIOS, Chipset
> drivers, VB.Net and .Net framework etc.) Of course,
> couldn't revert Windows XP Pro or DX9 back though. So,
> what on Earth is causing this problem? Is it hardware (I
> haven't changed any HW since last August), is it a WinXP
> update, DX9?? I hope someone out there knows!