Vista - Keyboard problem

Vista has suddenly developed a keyboard problem. When I click shift,
ctrl and right (or left) arrow, it used to select a block of text. This
has stopped working.

Two things have changed: I briefly installed a USB keyboard, but it
didn't work (it turns out I had USB Keyboard disabled in the bios) so I
plugged my PS2 one back in. Secondly, Vista installed lots of updates
today.

All other keyboard short-cuts seem to be working - any idea how I can
fix this?

Thanks