First things first; get your vacuum with creviss tool attached, unplug the power cord to computer, open that case and carefully clean-out the inside of dust bunnies, make sure RAM memory sticks are fully seated. Check that all exterior connectors are fully seated.

Order of probability -  Graphics engine failing, RAM stick faulty, power supply failing, motherboard issue.

Slow down take your time be  careful.

Others will help I've got to go............