Then run electrum again and hopefully it'll start now.
This worked, thank you!
Note that I also deleted ElectronCash folders.
i7 5500U
16 GB RAM
Electrum-3.0.3 as I wrote, just reinstalled the new version after I realized it didn't work.
Reinstallation didn't help though.
I upgraded to 3.0.3 recently on Win 10 64bit with no problems so I can confirm it should work. It's not that easy to diagnose when Windows just doesn't run something and doesn't give an error message.
It is working now
Try downloading the 3.0.3 Portable version, put it on a USB stick and run it from there... see if it works. If that does, and the installed version doesn't, then I suspect that for whatever reason the installed (and/or standalone) version is unable to create/read/write to the Electrum datadir or one of the files/folder in that directory... %AppData%\Electrum
I already added the folder to my AV and firewall exceptions list but it didn't help
Abdussamads solution solved the problem