It is an Nvidia Tnt2 according to this page:
http://h10025.www1.hp.com/ewfrf/wc/docu ... 07&lang=en
Try commenting out the DPMS line by putting a # at the beginning of the line like this.
DPMS handles power management and your system might not play nice with it.
to edit the file, do the following in a terminal window:
sudo gedit /etc/X11/xorg.conf
Save the file after you make the change and then logout. At the login screen, press CTRL-ALT-BKSPC to restart X.
Let me know if that works.
Some hardware combinations have quirks like this.