Unfortunately your coins are lost.
But if you want to find out what exactly happend, please answer these questions:
- Did you verify the file after downloading?
If not, check the signature. This eliminates the risk of using a malicious version of electrum. - Did you have a password set?
- Which OS are you running?
- Which version of electrum did you use?
- Did you already scan your PC for malware?
If not, do it.
This won't help you to get your coins back. But knowing what happened is the first step towards securing your coins better the next time.