MacBook Air shuts down

My MacBook Air 2015 displays a collection of tiny coloured rectangles on a black screen on startup, then shuts down. Maybe an hour or so later I can get the same result on a startup. This has deteriorated over the last week. It started with shutting itself down while sleeping and being difficult to start to this situation. I have tried the various resets, Vram and Pram with no apparent effect. Did take the machine into a local Mac shop which ran a diagnosis on it which showed a weak battery which was already known. Any suggestions would be appreciated, thanks

Couln't get any reliable resolution for the MacBook Air so bought the new MacBook Air M2. Very impressive. Couldn't let go of the old one so tried a few things. The reinstall on the OS didn't work since I kept getting a message that I didn't have enough memory. The more I deleted ,the more memory it wanted. Clearly not working. I deleted the HD and reinstalled the OS. Voila, a working computer. I did not do a file transfer from Time Machine since I didn't want to get my old problems back. I was surprised that this wasn't suggested at the Mac store. It was a little drastic since I don't have my old files but I will still have a functional backup computer for internet and mail. Thought this could be helpful to someone.