I had this issue and tried for months to fix it. Finally have it working normal. I changed MB, fan, memory and nothing. Still seemed to be heat related so found another fan that was actually new and not a used part. Laptop works like normal now. The first replacement fan was a used part. Looked like new but did not work correctly. Very hard to tell. The second fan was truly new and saved me from throwing this laptop out.

I have been dealing with this issue for quite some time. Cleaned everything. Replaced fan. Replaced MB. Replaced CPU. Replaced DC jack. Replaced Lan cable (different issue). Total reformat and reinstall. Have it working now but only with switchboard and on/off switch hanging out of case. When I reinstalled the switchboard cover it would die. Check your on/off switch and switchboard if you have one.