I had a PB100 that did the exact same thing - weird flickering screen/static noises and needed a firm slap on the 2.5" SCSI drive before it span up after years of not being turned on. I could never get it to boot reliably, and then I was given a PB100 with smashed screen so merged two into one. Batteries and "stacked" PRAM batteries were all dead, so I don't think that was the issue.

During this repair I was also fixing up a Quadra 840AV and SE/30 by replacing the capacitors from member trag; and noticed the PB100 also has the exact same type of leaking caps. First though I'd reseat the RAM and rebuild everything. Then I'd do the old "clean the board with metho" or put in in a dishwasher, leave to dry for a week and see what happens then. If it's any better, replace the caps.

JB