Macbook Pro keeps crashing

So i am having this problem where my macbook pro (early 2011 17") keeps crashing. It already had its motherboard replaced due to faulty manufacturing. But it started acting up again...

The problem was that it wouldnt boot most of the time but when it would it would run fine... then i typed in some codes in single user mode did some cleaning of the internals and checked the disk(hdd) with build in disk utility. After this it would boot and run fine.

But the keyboard gave up some keys didnt work and using it like that was no option. so i replaced the keyboard (and i was already afraid something like this would happen) and now i am running into problems again.... but not the same ones as before.

-The screen shifts and the mouse on screen goes to symbols in a vertical line.

-the macbook display sometimes goes to a dark grey screen with vertical lines in it.

-it most of the time crashes when i try to do something.

Ive already booted from a usb and formatted the HDD and reinstalled high sierra from the usb. This hasnt helped and the problems still occur.

Does anybody know what this problem could be? Thanks in advance