The HP logo implies it is very early in the boot up sequence. This is well before Windows start (I recall MS banning modified WinXP boot up screens). Since you already tried a boot disk (did you try BART? KNoppix?) I won’t suggest that. It also appears to be pre-POST, since you can’t get to BIOS. If you haven’t heard beeps (usually several repeating) then your system has failed to launch.
Seem that you have a hardware problem; hope this isn’t too old – still on warranty? There is a chance that the system is still in “factory mode” or similar. Call HP or find the schematics for your model (if you can find). you might have to change a jumper on the motherboard. I don’t know these directions for this, which change from each mbd.