I have a couple of Compaq Deskpro ENS C600 SFF computers. They both originally have a 500MHz Intel Celeron CPU each, socket 370. I tried installing an 800MHz Pentium III in one of them and nothing happened, except for the fan speeding up WAY faster than what can be set in the BIOS. Nothing appears on the screen. Then I put the original CPU back, and everything was fine.
The RAM is PC133 RAM, I believe it is SDRAM. One has 128MB of RAM and the other has 512MB of RAM, the same kind. Both machines do the same thing.
the new cpu ios not supported by those machines.
You can try using the old cpu and updating the bios and then try using the new cpu. If it still doesnt work then the cpu is not supported in the bios and thats very typical of a mass market pc (dell, hp...)