hi,
check this document first from HP. http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&cc=us&dlc=en&docname=c01087277#c01087277_identify
btw have you tried uninstall and reinstall of video drivers? if not, try to uninstall and reinstall the video drivers.
if symptom persists, try to boot another operating system like linux in live CD.
check this document first from HP. http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&cc=us&dlc=en&docname=c01087277#c01087277_identify
btw have you tried uninstall and reinstall of video drivers? if not, try to uninstall and reinstall the video drivers.
if symptom persists, try to boot another operating system like linux in live CD.