DS416 power off? Just flashes forever!

[Quantillion]

Hi,
I need to replace a HDD, so I've deactivated it & now need to power off to replace the disk. "Replace a drive" instructions just say power off & replace the drive, but the blue On/Off button just flashes forever (= a week!) before just remaining On!
Should I just unplug it?

 

[Telos]

Should I just unplug it?

At this point, what other option do you have?