I'm trying to help you systematically by eliminating known video problems.
You should try with another monitor and let us know the result.
(With HP machines you should not update the BIOS unless it is REALLY necessary.)
{From a thread 9-01-2008
We try to get people to understand that flashing the bios is not needed unless it's having the symptoms described in the bios update.
To reload the factory BIOS settings to the setup default.
Press the F5 function key
Select Yes of OK
Press the Enter key
Press the F10 function key
Select Yes or OK to save the default settings.)
---++++Only read the manual as a last resort++++---.