I had the same prob. with a fairly expanded 3000, suffered for months with it. I've done two things that seem to work. First, I cleaned the zorro connectors thoroughly, like Framiga said, both genders. Second, the chips under the "Power" & "Hard Disk" LEDs on the MB get very hot. I simply installed a mini fan blowing directly them.
Result: most of the problem is gone, however, when I've been tinkering inside and then re-assembly the machine, sometimes I wont even be able to boot. I have to unseat the zorro daughter board and expansion cards and reseat them again and test the system. It seems I can still have an intermittant, especially if I tighten the header-panel screws in the back. Usually, if I can get the cover back on with out introducing a bad connection, the machine wont crash for months.
