i have this problem too.
i have install electrum 3.0.3 at 26.01.2018
after 2 days i have see a output transaction and all my bitcoin lost.
don't use electrum! shit!
From where you downloaded? Did you checked the PGP signature?
from official site and not 3.0.3 version but 3.0.5
Version 3.0.5 didn't contain any vulnerability.
The most probable scenario is that your pc got infected by malware which led to a theft of your coins.
Did you check the signature? Or at least comparing the hashes? This could exclude a malicious version of electrum.
Was your wallet password protected?
You should definetely run some anti virus checks.