First thing, check the fuse where the wall power plug goes. Don't have a multi-meter? Just put the replacement fuse in and see if that works. Hopefully its that simple, but probably not..lol
I had similar issues with low voltage not getting to the main circuit board from the power supply circuit. If you have any experience with electronics, pop the case open and look at the power supply circuit (its right next to where the power plug inserts). The board is installed with a couple screws and wire connectors. No de-soldering required to remove it. If you think you can replace it, register your product, make a support ticket to Presonus, and ask customer service for a new power board (P/N: 410-X20PSAC). I think they cost about $35+shipping.
If you don't think your capable, just buy the new power board anyways and bring it to any local electronics repair place. Shouldn't take them more than 10-min.
As soon as I installed the new power supply circuit, in my firestudio, it fired right up and works as it should!