Vista (Ultimate) has 'lost' access to all its in-built drivers?

I am having problems installing devices on Vista. It seems that everytime I
install a new device (this issue may be confined to USB devices) Vista simply
cannot recognise it. I have to manually point the browse for drivers to
c:\windows.

The problem goes a little further than this in that Vista cannot see it's
in-built drivers.

I have a HP Deskjet 6122 printer, which HP haven't got any Vista drivers for
yet. Their support site says to install it using the drivers for the Deskjet
990c which are built into Vista. This works fine on my g/fs Vista PC, but on
my PC, when I click 'Add a Printer', 'Local Printer', 'LPT1', I get the
message 'Unable to find any drivers for this device' instead of a list of
Manufacturers and their various drivers.

Is there any way to fix this?

I REALLY don't want to have to format and reinstall Vista as I have a load
of dev tools installed, as well as lots of video editing stuff and a nearly
full 500gb hard drive which will be a royal PITA to backup onto DVD.