As it ran W7 it could be an aging PC in need of basic work such as fan replacements, heatsink compound, BIOS update, BIOS settings, drivers and more. I can't tell from the details so far except it sounds like the usual.

As to your question about Malwarebytes and Windows Defender it's a common mix and I have yet to find it to cause any issues.

Let's try a look at the PC with the usual Web Speccy Report. It will show some common areas in a single report that members can comment on. Here's how:
https://www.piriform.com/docs/speccy/using-speccy/publishing-a-speccy-profile-to-the-web