I bought a PM 8600/300 from a thrift store. When I try to boot it, the drive spins up and it plays the "bawoom" sound but the screen remains dark. usual symptoms of a dead PRAM battery, but that's not it.
replacing the battery
resetting the CUDA (sometimes works to get the Mac booted)
resetting the PRAM
trying different HD's and RAM sticks
disconnecting the Hard Drive, ZIP drive and trying to boot from a CD
reseating the processor card
trying different keyboards, mice, and monitors
No SCSI, Serial, or other devices are hooked on to it. It's all stock, except for 1 RAM SIMM that works (I tested).