my preamp wont power up

You can turn the screen off on the Ref 5. But there is still a green dot lit in the center. The screen default is on.

If it worked when it was unplugged, my guess it is something simple. Unless you kept it in a bathroom I doubt the humidity is the cause. Is the power cord pushed in all the way? Are all the tubes seated properly? Is the 6550 in the power supply lit up? Do any of the tubes light up? What exactly does it do and not do?

There was a problem with the power supplies on some preamps and soured components. They used 2 6h30s in the power supply which not always aged at the same rate. This could affect the sound. So ARC offered an upgrade to replaced the 2 6h30 tubes with a single 5771. I know my CD7 was upgraded this way. I don't believe the Ref 5 had this problem Though.

I still think it is something simple. I would try moving the preamp to another room and use a different power cord. Just to see what happens. If that fails I would call Kal at ARC. If you bought it from a dealer you could have him take a look at it.