First, try looking at the logs.
If you are using Xorg,(the X server), then look through:
/var/log/Xorg.0.log
Look for text beginning with 'EE' and 'WW' (errors and warnings).
This is the first place to start.
Then, look at your xorg.conf (or equivalent, google for whichever X server you use).
/etc/X11/xorg.conf
This file is what decides which drivers get loaded for the display.
I googled for
"Linux drivers for the 845"
and ended here:
http://www.intellinuxgraphics.org/install.html
Like I said, first look at the log. Then google for the error/warning messages.
(I assume you have access to another machine ..since you were able to post this)
If you are still lost, please post the error/warnings and your xorg and the output of lsmod