qnap ts-112 and multimedia station slow and blocked

[enjoyto]

Hello, first of all I apologize for my bad English and my little knowledge of NAS.
I have a Qnap ts-112 with one disk seagate ST2000DM001, the NAS is connect to a router Netgear DGN3500 and i access to NAS by a Mac, PC windows Seven and IPAD.
At the first i have installed the firmware 3.7.1 and i have formatted the disk EXT4.
I have activated the web server and the multimedia station, i can acces and login to the page of multimedia station.
I have created tree subfolder in multimedia folder ( video, foto and music).
I can see this in the multimedia station but just i select a video or a foto folder the multimedia station not respond and the system administration is very very slow!!
i can see on the panel of NAS that the led of HDD is continuous bliniking! the only solution for me (i am at the first experience whit NAS ) is the shutdown the NAS.
someone could help me identify the problem?
i have try to downgrade the firmware to 3.6.1 and to format the hdd in EXT4 but I had no results.

Thanks in advance to all who help me!
bye!