How do I get my laptop screen up and running?

I have a Lenovo Thinkpad 530c that has been around for a couple of years, but I would like to use it even longer. Currently, I observe the following phenomenon: When I start the laptop, the normal start-up screen is displayed for a few seconds (i.e., screen and control of the screen are ok), but then everything turns white, purple, striped… The pattern recovers again and again. What can this be? I've already replaced the monitor cable, but as expected, that did not change anything. Currently I have to work on an external screen.

The display is defective you have to exchange.

If the external monitor runs without problems then the graphics chip o.k.

So probably the TFT broken.

Something in more detail please. As I have described, it works normally for a short time.

Must the WillEsWissen64 to vote after the TFT when exactly it comes to de problems only in the windows he brings errors in the bios too?

For a long time, I was sure that it was a loose contact, because the white / colored screen appeared again and again and I only had to wiggle a bit on the screen and ran again. Then I had the problem described above for a while, later it was back to normal.
In bios I mean, the screen goes normal.

Then I would create a linux boot stick to work with for a few hours because if everything in the bios is normal it does not sound like hardware