Could be a CPU or a motherboard (you might want to look for any bulging capacitors on the MB).
With all the cards out, Ram out, and all the drive cables disconnected. Just motherboard, CPU, power supply and front panel (and power to the floppy so your PSU has a load) should give you constant beeps (no ram message) If you don't get any beeps, then either the CPU, MB or PSU is bad.
Now, what kind of computer is this? because I can't tell you how many Compaq Presario 5000 computers have come into the shop to be fixed and had bad motherboards.