Macbook A1181 Shuts down after a few minutes My dinosaur macbook randomly shuts down. I've reset the SMC and it still shuts down. Even the computer doesnt know its coming because you can hear the arm inside the hard drive clunk as it shuts down. If you leave it sit it will last longer on the next startup. Sometimes it wont even make it to the startup chime.
Try to boot macOS from external Hard Drive or SSD. If it's stable your internal disk is damaged.

Read about external startup here.