T520 HD3000 Freezes screen

Hi Guys :D

i have a T520 Lenovo with the following specs:

i7-2760qm HD3000 iGpu 16GB Corsair Ram 256GB SSD from Samsung

Everything is working beside from the weird Freeze that I get If I minimize an app like Safari, etc.. the only Resolution is too Shutdown the notebook with the Powerbutton .... it happens randomly after 5min-2h i dont know hol to attach an Picture from the Freezing screen?

I have been searching for a month for the solution and found nothing....