i have a hp pavilion with athlon2 , im trying to upgrade my cpu , i just bought a phenom 2 x4 840 (deneb) and the specs say yes i can , but when i put 840 in , i get no boot, it starts up , i hear fans and hd tryin to boot but no vid.
If that is the same board as yours, search for a bios for it. Check your bios and see what version it is. Report back. If there's a newer one available, it may be necessary for the newer chip to be recognized.
Here's one I found for version 5.20 circa 2010: http://h30434.www3.hp.com/t5/Desktop-Operating-Systems/... I don't know which version you have now, but I'm thinking it's too old for that processor.
You would have to re-install the original CPU and update the bios. Then change CPUs.
...and send that link to the CPU upgrade list you found, if you would.