A bit of history about this computer:
I received it in late 2012 as a main video editing rig, and I've definitely broken warranty on it years ago (a little about this later). I've installed so many different kinds of modification software, it's ridiculous. The trackpad died long ago, completely pronounced dead by a professional repairman at Micro center.
A few years ago, I opened up the case to do a mass cleaning and dusting of everything since by that time, warranty had expired a year prior. This turned out a success, though I sent it into Micro Center about a week later to get a new screen when it turned out the connection for that was loose. The display was fixed very nicely and a week later, I upgraded the hard drive to a 1TB (which has proven very helpful). I also replaced successfully the optical drive with a stronger Blu Ray one.
This thing has powered through some things it was never built to do, such as a 3+ monitor setup, quick animation rendering, complex After Efffects projects, and live game streaming. I's also been traveled many times on planes, mostly through a backpack, though this last time I used a suitcase (more on this later). I moved from the US to the east of England, though I also use it often in Northern Ireland. This has become more prevalent these days, so the computer gets even more travel time.
Short of overclocking it or adding the extra drive, I'm not sure what else I could also have done. So, I won't be too shocked to hear anyone say that it's past its final throes. However, if this issue is still fixable, I'll take it. I've been surprised many times.
Now, on the way to the US, I put the computer in a suitcase because I didn't want to have to deal with taking it out during security, and carrying it around from train to train. It arrived and worked perfectly fine in the US. There, I also got a small internship which would require me to carry the computer about every week, resulting in even more travel time. It was heavy each time, but showed no issue except for a graphics driver issue that was quickly taken care of after an update.
After coming back to the UK, I powered it up to find myself looking at an entirely green screen with the exception of a few changing pixels. Remembering the last issue with the monitor, I opened up the case and the monitor and resecured the connections. This turned out a success (no more green screen) but now the computer just shuts off after the little white rectangle blinks. I'll get indicator lights even before hitting thr button and the fan will go on, but it's not held power. I have tried resecuring the connections from the keyboard to the motherboard, but that doesn't seem to have done anything. I have also tried taking the battery out, which yields the same result.
I would not be surprised if this is it, but just in case I'm missing something, that could be helpful.