Apparently computer guy can get it to turn on in Diagnostic mode but only turns on 20% time in normal mode
Might I suggest you try another computer guy?
Have they explained what they mean by diagnostic mode? Is this windows safe mode or is it a BIOS diagnostic mode?
Do you know if the machine has an SSD? (What laptop is it?).
When you say won’t power on, exactly what happens?
I am zeroing in on these because if it is having issues intermittently, but starts up in whatever diagnostic mode they are using, there is a chance it’s not a critical component. Hard drive is the first culprit I would be testing followed closely by memory.