Excellent game!!
The idea is very simple and fun to play!
The simple art remembers MS Paint, and the sound effect matches with it as well.
I had the same problem as Cortop said. When I open the .exe from the second time onwards, the screen starts all grey, and when I minimize and maximize, it shows only the bombs numbers.
Here are the screenshots:
https://postimg.org/image/t3prsyvo5/
https://postimg.org/image/7vc3bjh79/
After that, the first time I ran the .jar file it had the same problem, but after the second time it worked fine.
Congratulations for the game!!!