how about the CPU? Original or was it upgraded. The daughter card can't be from the Mach V machines as those will not work (such as the late 9600). The CPU itself could be causing your issue and I assume your reseated it as well. and you made sure it was all the way down?

Also put a PCI Video card in it. your onboard video could've died. It's rare, but it can happen.

So you could take the 7500 CPU daughtercard and throw it in, and then if you have a PCI video card throw that in. if it's got a G3 upgrade, make sure the settings around right for the CPU. Also keep in mind that if the CPU expects a certain bus speed, and it doesn't match the PowerBase, the powerbase may not work or start. Especially if the timing is messed up, It may barely sync enough to cause the chime, but get unstable immediately after. You never know.