You don't really talk much about the condition of the unit, or it's age, but a few observations... these units are constructed from a bunch of boards which are linked together via ribbon cables. If you live in a humid climate and / or have bumped the unit around a lot, something may have become corroded or disconnected. Additionally, these units have horrible ventilation, no fan, and use components that are right on the razor's edge of being UNDERspec-ed for the application. The power supply is a known weak point, and like most modern electronics, the power supply does not just put out a single voltage on a single rail, it puts out 4 different voltages on various rails at differing current levels as appropriate to power different boards in the mixer. As such, a failure of one part of the power supply might leave some things functional and other things not.
Regardless, troubleshooting by a reasonably qualified technician is more than likely required.
I've attached a document that should let a decent tech repair the power supply, if that turns out to be the problem, despite the fact that no schematics are available to the public for the rack edition at this time. Credit: Electric Things
You can also find the X32 full 32 channel console edition schematic in one of my previous posts, and some of the audio boards are very similar in design to the rack edition, as it the support circuitry for the display panel.
Good luck!!
