LS441D stuck in startup after installing fourth drive

[Ghidorah23]

I have an LS441D which has been running with 3 4tb drives (No RAID configured). Last night I installed a 4th 4tb drive, after turning on the NAS all 4 drive LEDs come on but it then gets stuck at the point where the power light flashes blue. I can no longer see the NAS in Navigator or on my network. It has been this way for 5 hours now, when installing the other drives it only took a couple of minutes to turn on. I am using windows 10.

Any advice on how I get the NAS to startup and be visible on the network? I have tried turning it off by holding down the power button, but it doesn't respond.

[oxygen8]

"I installed a 4th 4tb drive,"

1. Delete all partitions on the new drive
2. MBR or GPT ? all 4 drives must have the same entry

Point 0. from

http://forum.nas-hilfe.de/buffalo-technology-nas-anleitungen/anleitung-tftp-und-firmware-flashen-mit-bildern-t903.html

[Ghidorah23]

After trying some things out, I see the following:

1) With the new HDD (drive 4) removed, the LinkStation boots up as before and can be seen on the network. Startup takes a couple of minutes.
2) Taking out drive 3 and placing drive 4 into the drive 3 slot, the LinkStation boots up and the drive showed up as "unformatted". Format of the new drive in this slot worked OK (GPT used to match the other drives). The LinkStation shuts down and restarts OK, startup takes a couple of minutes.
3) Placing drive 3 back in its original slot, and placing drive 4 back into the drive4 slot, the Linkstation seems to get stuck on bootup (blue light flashing rapidly)

So basically as long as the fourth drive slot is empty it seems to work OK.