Given its age, has it ever had a thorough internal cleaning (including replacement of the thermal compound/pads that sit between the heatsinks and heat slugs on the GPU and CPU?  If not, that's overdue.  While you're in there, you can change the reserve battery. Service manual: [URL] Battery: [URL]  
I have an Inspiron 5577 that shuts down randomly with a click whenever the fan spin up and temperatures rise. When I turn the laptop back on, it would throw a CMOS battery error. Is there any fix to this?
Dell Inspiron 5577 randomly shuts down during moderate use