sounds similar. I have 2 SE30's, one has been mine for many years and the other is very recent. The older one worked fine for years, then developed simasiMac like stripes every now and then; sometimes it would work fine, sometimes not at all and sometimes after a period of minutes.

Now the older machine has had new caps and doesn't work, same horizontal stripes, but no startup noise, no drive movement or anything. The second machine has worked in the past few months but has recently stopped when used with a IIfx Rom. Same again, horizontal stripes, no drive activity. I'm reluctant to change the capacitors on the second SE30 although I suspect they need doing, other than that I have no idea how to get them going.

If I ever get either of them to work after this, I'll let you know how.