It happened because the software stopped me from proceeding you fucking idiot!
That's not completely true.
The electrum server which you were connected to (which can by run by anyone who wants to) didn't broadcast your transaction.
That's not related to the electrum wallet itself.
Instead of simply clicking on an URL to download software which you didn't even verify the signature of, you could have simply connected to a different (non-malicious) electrum server.
I don't know how often you already read that here on the forum.. but..
Verify, don't trust!
I havent receive any popups and i downloaded from their site about two years ago.
The fact that you didn't update a software which holds your money for about 2 years, is already pretty bad.
Unfortunately there is no way for you to get the money back.
Since you didn't download a malicious wallet trough a phishing attempt and since your wallet is password protected, i'd say that the most plausible explanation is that your computer is infected with malware.
Did you download any half-way-shady software within the recent days ?
Do you use a legal copy of windows (cracked versions almost always have backdoors built in) ?