Lost video driver for Scenic P300 i845GV

Hi,
Fixing a friend's PC. Plugged in a new monitor (HP w1907v) to a Scenic P300 i845GV and although the resolution was initially good, I was called back 3 weeks later as the resolution deteriorated (reason unknown) and dropped to the lowest resolution (4 colours). I couldn't improve this via the Control Panel in Windows XP Pro (didn't give me the option).

Therefore I used the monitor install disk (though I haven't needed this in the past with this screen). Again, this didn't help, so I uninstalled the monitor but in doing so, it seems the generic plug and play display driver was removed. When I plug in any monitor now, you see the Windows XP progress bar on bootup, but the screen goes blank when Windows has started (you can hear the XP startup chimes). I've tested this with 2 monitors.
Does anyone have any idea how to resolve this, please? Has the display/graphics driver been deleted? If so, how can I re-install this? We don't have the XP Recovery disc.
Many thanks,
Andy