XPS 13 (9350) Problems under load... please help

Hi, After opening the back of my XPS, since it was making a weird noise (the fan cable was catching against the fan). I've been having problems with my XPS... The laptop runs fine in idol. I can keep it on a web page, document or any other "stationary" task. However, as soon as I play a video, game or stress test the laptop crashes. I've managed to do this whilst running the F12 diagnostics, and it crashes on both the memory and CPU stress tests. No problems occur on the other tests. I've also run it through the Intel Tuning Utility to monitor levels. When the crash occurs the screen freezes and at that moment on both the BIOS diagnostics and the Intel program no overheating/throttling seems to be occurring. Although it does crash at about 87c on average. Which I think is hot. However, since the fan doesn't come on until 90c then perhaps is normal?? I have run Memtest86 for a 5 passes. Without crashing or any errors. In regard to my fan cable, I have dismantled the whole fan assembly. There is no problem with the cable (no bare cable) or debris in the fan. So don't think it's that. This problem occurs with and without AC attached. It also occurs with and without the HDD installed. Don't really have the financial ability to get a new motherboard as am a student. Thanks for reading, Rob.