3 years of XPS 9560 slowing to a halt, Integrated GPU at 100%

I beg the help of you wise people. I have only been able to use my dell XPS 9560 for basic tasks for three years.

Problems experienced:

After around 1 minute of starting to game (literally any game that requires any effort) or sometimes even when I have multiple tabs open and am trying to watch more than one video, the following occurs:

- 80-100% load of the Integrated HD GPU 630. Processes responsible appear to be "Desktop Windows Manager, Client Server Runtime Process"

- Laptop becomes unusable for upwards of 20 minutes

- I also see that every time I move my razor gaming mouse quickly across the desktop, the above processes seem to react and jump up another 10-20%.

Solutions attempted (all with no effect)

- Re-booting windows, doing a clean install

- Cleaning my internal cooling fans on the laptop

- Using NVIDIA control panel to ensure that the GTX 1050 was employed by most apps.

- Tried to get all updates for drivers and firmware etc as I can (using dell support assistant and online)

- Run multiple virus scans (e.g. with bitdefender)

- Reducing polling rate of my gaming mouse (made the quick mouse movements described above only load the GPU to 10% instead of 30% but had no effect on the overall problem).

- Playing around with desktop scaling as apparently that may have had some effect.

Things that do help:

- Turning off my computer for a long time, after which it takes a little longer to stop working

- Used to be that disconnecting from my external monitor (Dell Ultrawide U3417W) helped but that is no longer the case.

My Device Specifications:

Laptop: XPS 15 9560; i7-7700HQ CPU@2.80GHZ; GTX 1050; 16GB RAM

External Monitor: Dell Ultra-wide U3417W

Please, if you could offer me any help that would be amazing. Please also bear in mind that I'm not very good with computers, so if you suggest something could you avoid acronyms and treat me like someone who knows nothing. Thanks!