Same thing happened to me two months ago, same diagnostic, same behaviour of PC as you described.
My friend repair it, and said :
Too much dust in fan tunels, because of too much dust, temperature was too high and all the contacs on Video card was weak.
He has repair all contacs on Video card with Soldering and clean PC from dust.
http://www.youtube.com/watch?v=bnkQNmKauEc
here is video on youtube that i saw first, and after that i realise what can be problem with my PC, and than i brought my PC to my friend.
My laptop is HP Pavilion dv 9000, i think Compaq is the same build or manufacture, so it is the same pc actualy.
hope this helps
Sorry guys for my english, i know it sucks 