your monitor is not getting a signal from the pc
now we have to find out why
unplug the pc from the A/C
look at the capacitors on the mainboard. They are those little metal cans sticking up on end.
are they puffed out or leaking electrolyte ?
remove the ram, do not put back in right now
plug in the A/C line to the power supply
turn on the pc, you should hear beeps, this is the PC not finding ram,
if you do not hear this the mainboard / ps could be bad.
unplug the A/C
put the ram back in
plug a/c back in