After adding some new drives, when I flicked the power the unit would keep turning itself on and off in a loop. It stays on for about 5 secs then turns off, then turns on again and repeats.

 

So I removed cables and parts one by one and still get the same thing. If I keep the 12v ATX plug un plugged, the power supply will stay on. As soon as I plug the 12v ATX plug in, back to square one.

 

The unit has been working great up to this point.

 

Any advice here?

Try checking the boot sequence in the bios.  I added a new drive to my server last week and the bios setup changed the boot sequence on me.

 

Make sure you are still booting from the flash drive.

 

If not - you could be under powered in your PSU.

 

Just a couple of thoughts.

After adding some new drives, when I flicked the power the unit would keep turning itself on and off in a loop. It stays on for about 5 secs then turns off, then turns on again and repeats.

 

So I removed cables and parts one by one and still get the same thing. If I keep the 12v ATX plug un plugged, the power supply will stay on. As soon as I plug the 12v ATX plug in, back to square one.

 

The unit has been working great up to this point.

 

Any advice here?

Sounds like the power supply cannot handle the additional load.  What specific model/brand is it?  How many hard disks are you powering?

It wasn't even doing POST, no beeps, literally on for 5 seconds then off in a constant loop and thats with no drives or anything plugged in, just the bare minimum to power the board.

 

I removed the CMOS battery and used a jumper to clear it. Took a couple of attempts but now its staying on. I'm been running the unit headless so I can't see whats going on, will pop out and borrow a monitor from the office. Maybe something funky happend when it powered down.

 

What were the chances.....