Computer boots itself when power cable is plugged?

the computer does this and then i hear 1 long continuous beep. i have an ami bios and the monitor says no display. very frustrated. can anyone tell me if my mobo idead or if my psu is dead? also when i remove the ram and turn on the computer, i dont hear any beeps. i only hear that beep when i use my second psu.my main psu doesnt beep.when i have it installed. also when i plug in something to the ports on the back, like the ethernet, the port lights dont come on ;like theyre supposed to.