WD Sentinel dx4000 Loading OS error

Hai WD Community,

I have an error in my WD sentinel dx4000 suddenly, after a reboot the device is not able to load OS.
It shows at being>> STARTUP INITIALIZING…>>then INITIALIZING OK SEARCHING…>>then LOADING OS PLEASE WAIT…>> After that its going back to STARTUP INITIALIZING and so on.

*4x drives
*Windows storage server 2008 r2 essentials

please somebody support me for this issue