It doesn't get near boot-up before it restarts.
You could run an OS (Linux etc) from a USB stick to rule out Win 10 or not?
You could run an OS (Linux etc) from a USB stick to rule out Win 10 or not?
It doesn't get near boot-up before it restarts.
I've tried it with an alternative cable to no effect.
Where did you get an alternate cable for that connection?
Usually the wires are permanently connected to the PSU, never seen an alternative connection from PSU to mobo.
have you tried a bios reset ?
it could have become corrupt for one reason or other
Well, the OP said he'd decided to get a new bare bones system, so he'll have the option of testing the old system with the new PSU before he fits it all together. If it's another modular unit, it won't be a big job.