My Net 900 Central: Replaced internal HDD, HDD is not recognized by router! Why?

Hi!

The original HDD went out of order, so I built in my old 2,5"" Samsung 400 GB. HDD is not recognized by router, I don’t know why… I guess this problem is also the reason why suddenly I can’t activate Remote Access, I get the message “server error”.

Can someone help me to run the new HDD inside my router?

Thank you 

off topic, but what kind of HDD was it? 1TB 2TB? Model No. is possible?

I am trying to figure out a good use of 2TB I have but dont want to open the router and void my warranty.

Thanks,