Total Blue screen

[N181RV]

Three times, I have accidently hit a key or keys that have made the screen go totally blue. it has happened when lighting was dim and I was shutting down for the night..
First time it happened, I accidently got out of it without knowing what I DID. The second time, I uninstalled hoster and reinstalled it and it came up ok. This time, uninstalling and re-installing didn't do the trick.
I can shut the computer down and restart it, then restart Hoster and Hoster screen comes up all blue again
Does anyone know what I hit to make it go bad, or what I need to do to bring it back.
I am running win 7 with 8 gigs of ram. It is not a Hoster fault the best I can figure out. I think I am hitting some key or combination of keys and it immediately goes to blue screen.

Thanks Phil