This started about three days ago, but it was just a green line on the very top of the screen (it looked like that red line when you mispell something in word, but green). A few hours ago it started flashing green and pink lines all over the screen, most of the times it last less than a second, but sometimes it goes for 1, 2 seconds. It's also pretty frequent.
I have tried a bunch of solutions I found on dell's website but none of them worked. My graphic drivers are updated. I'm going to try to connect the laptop to another monitor to check if it happens again, but only tomorrow because I don't have a cable with me, so I wanted to try to find some help here. Hopefully I can solve it tonight.
Your best bet is going to be to test it with that external monitor. If it shows fine on it, then your attached display, or the cable that connects it, are the culprit and one or both could need replacing.
Now if you get the same issue on the external monitor as well, then your graphics card/GPU is on its way out and would need replacing. Possibly meaning the motherboard would need replacing.