MacBook13 mid10, irregular occuring grey screen, no text, no reboot, just hang

Hey,

since a while I have irregulary a grey screen. It happens whenever it want and irregulary. I can leave the computer and go back and have a grey screen. It is in IDLE or load, doesnt matter. When there is itunes playing, it keeps on playing the music as would be no grey screen. The keyboard and everything is not responding.

I have third party ram (checked it, isnt the problem) and intel ssd 320 with 120gb as subsititution for the disc drive. Mostly i ran the macbook on my Dell 2412m via displayport but also had the problem while on other monitors. I rau Mavericks 10.9. Usually i ran only Skype, chrome, dropbox, xtrafinder, alfred and istats.

When the grey screens (sometimes purple 😉) comes it have no errormessage or log text. Just both screens are grey.

Do you have any idias what it can be?

Thank you very much!