Readynas stuck, but activity LED blinking

Hello,

I installed my 104 with 4 disks and replaced one by a larger one.
It was quietly reconstructing the volume so I decided to add some data's to it.

My data is on a hard drive so I made a backup task and launched it from front USB.

Since then I lost contact with the front view interface and the front display won't turn on.
Pressing on the power button won't help.

The activity led keep blinking, so I don't want to damage by turning the power off...

Anyone experienced the same thing?

Thanks

Guillaume