IntelliJ, Alt+Enter doesnt work

"Well, it means IDE doesn't see the shortcut for some reason. Probably it's already used by some other application or the operating system. – CrazyCoder 25 mins ago "

i closed all applications and it turns out that, Facebook GameRoom, running in the background, somehow is the reason the shortcut doesn't work, i have no idea why, but thats the solution

many thanks to CrazyCoder

It was working earlier but it stopped working due to unknown reason,

One workaround is Try fn+Alt+Enter

I had the same problem
and it turned out to be the keyboard language in Windows, It wasn't english,
so just make sure you are on English