1) Recap it. Check for any broken traces or cracks in the chassis while doing so.
2) Inspect the flyback for cracks or a pinhole above the focus knob (WITH THE POWER OFF). I've seen quite a few still work with no lightning because there isn't anything close enough to arc to - that is, until you reach back to adjust the focus.
3) Listen for any faint "tick-tick-tick-tick"ing, as that would indicate a bad HOT.
4) Check the B+ at TP202 (not to be confused with the Video B+ at TP203). It should be about 117-118vdc.
5) Check R765 (open), R760 (open), Q708 (shorted), Z705 (shorted) and D710 (shorted). It's a common "no start-up" issue on the U5000 to have one of those resistors go bad and keep the monitor dead. Sometimes that causes some of the other parts to go bad also...