Still getting nowhere. Block explorer reports no transaction record. The seed may be off, but I am doubtful. I carefully printed it on paper in a notebook with the original setup. I'm wondering if the problem was that, after setting up the Electrum client to receive income from my miners through the EMC pool, I left it running for a long time without closing Electrum. Perhaps the transactions weren't being logged continuously? When the old nettop failed, Electrum may have never been shut down since first setup.

I would be happy to mail the drive from the old machine to Electrum's developers if they want to examine this further. It powers-up but I have no other hardware at hand right now that can talk to a 2.5" SATA. It has no particular value itself and it was a clean Linux install with no personal information on it other than what's in the Electrum files.

I will look for a block explorer to try. When entering the seed words, are they intended to be space separated or return separated?

I've just encountered the same problem. Was using Electrum on an old Linux nettop to setup some hobby miners and, alas, it gave up the ghost. Setup Electrum on Mac and restored with the seed from the other system and it shows a zero balance and reported no transaction history. Addresses are there (though I have little way of telling if they're the same addresses...) and autoc-onnect seems to be working fine, I see the synchronization work periodically, but no balance. About .01 BTC lost so not a disaster, but certainly a confidence killer.