What wallet version are you using, if you're on an older one, update to the latest one and see if the problem gets resolved. It happened with me once when my system got bsod (faulty ram) and I figured it might have corrupted the blockchain_headers file due to electrum not being closed properly, so here is what I did, you can try and see if these work for you.
Click the network icon in electrum (red/green light at the bottom), select Auto_Connect>OK, close electrum, go to the .electrum folder, you can find its location here:
http://docs.electrum.org/en/latest/faq.html?highlight=location#where-is-my-wallet-file-located , rename the blockchain_headers file to OLD_blockchain_headers, restart electrum and let it run and sync for a while as it will download the blockchain headers file again and when its done, your history should appear back. Or you can simply, rename/move the .electrum folder somewhere else and then re-store your wallet from seed.