my preamp wont power up

Make sure you have power at the AC outlet. Sometimes those outlets are on a switched circuit. If so, flip the switch.

Also, if it has a detachable power cable, make sure it's plugged all the way in.

More info would be helpful. What make/model of preamp?

Thanks,we have power.Im wondering if its the micro proceesor.The pre is a ar reference 5

Can you look inside and see if the tubes are lighting up, or is the unit absolutely dead? I'm pretty sure you can turn the screen off.