Before giving up, here's another simple thing to check. I'm sure you knew this already, but just in case not...The SE/30 requires RAM to be installed in groups of four, not groups of two. What is your current configuration? How many simms of what capacity in which banks?

For details on acceptable configurations, see http://lowendmac.com/ram/se30.shtml

I hope it's something simple. The SE/30 is a wonderful machine.