[MpG]

After a period of inactivity, I would expect heat or your PSU to be two of the less likely culprits, since both are more likely to cause problems during heavy activity.

I'm not seeing any red flags with your hardware. As annoying as it can be, you might want to give some serious thought to doing a reinstall. It amazing how much crap can accumulate over time (even when you're properly uninstalling/organizing everything) and it's not unthinkable that a 'perfect storm' causing those shut-downs might have inadvertently been created.