Inspiron 7520 screen is white after replacing CPU fan

Hi, I followed a YouTube video to replace the cooling fan in my Inspiron 15r SE 7520. The process went well and was pretty easy (my first time opening up a computer). The new fan works well and is quiet, and my laptop no longer turns itself off when it gets warm, which was the problem. However, now something has happened with the screen. When I turned it on for the first time after opening it, I got a sad face screen and an error message, something to do with drivers I think. It said it would restart and had a %complete counter and a QR code. I went to grab my phone to scan the code, but after about 30 seconds the screen went totally white. It's now like that permanently. I opened it up again to check I hadn't bumped a cable for the screen, or anything like that, but after triple checking I can't see anything loose it damaged inside the laptop. It works with an external monitor from HDMI, and the white screen is constant and not flickering at all. The screen goes black momentarily when you plug in the monitor. It seems pretty weird timing for it to be a totally seperate hardware problem, like a loose connection behind the screen. And it also seems weird that the screen worked fine for 30 seconds or so. Could it be a non-hardware problem? Any help hugely appreciated, I'm pretty much a novice. Thanks, Tom.