Windows 8.1 restart problem when using hdmi cable

I just purchased a new computer (medion) with windows 8.1. I connected a hdmi cable from my computer to my Samsung tv. When I play a video from youtube in fullscreen mode my computer restarts. I first get a blue screen with the following message: system_threat_exception_not_handled atikmdag.sys
Then my computer restarts as usual. I checked my graphics driver and it's new and updated. Also removed Mcafee and replaced it with Norton.
Please help.