Got a machine Presario 5002us that does nothing when you start it.
No bios screen, no monitor, no keyboard.
Power supply checked out okay
Cpu fan is running
I disconected everything but the videocard and cpu and memory. No boot
Switched out vidoecard
Switched out memory
I am thinking bad cpu or motherboard.
Do I dare to reset the bios to see what that does?

Well, it's either the mobo or the CPU. My guess is the CPU even though typically when one is fried the computer will just keep going throug ha cycle of starting up and shutting down. Also, do you have any old cards laying around? I had a very similiar problem and it turned out to be the video card. It's worth a shot.

I did switch out the video card with a brand new one. The only diference I noticed was that the monitor light stayed green

It won't hurt to clear the CMOS, though I doubt that's your problem, I'm inclined to agree with welco.

cleared bios and changed battery. Still no bios screen

I wouldn't spend too much money on it.

You can buy a new computer with current technology, a larger processor, etc for $300.