Display first flickered; now massive errors

It started some weeks ago; My screen went randomly black for a verry short time and then turned on again.

Now my screen is flickering and some parts have stripes on it.

Here is a picture and a video:

Can it be that the display cable has a loose contact?

Thanks for your help

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 3

crwdns2933313:01crwdne2933313:0

crwdns2933897:0crwdne2933897:0

Hook it up to an external monitor to help isolate the problem. If the picture on the external is OK then the GPU is good.

crwdns2934105:0crwdne2934105:0

crwdns2889612:0crwdne2889612:0 4

crwdns2942205:01crwdne2942205:0:

The picture on the external monitor is OK ... so I suppose its a problem either with the display or the displaycable...

crwdns2934271:0Yan 5, 2016crwdnd2934271:0 robzh crwdne2934271:0

iMac Intel 21.5" EMC 2544