DS-7608NI-I2/8P reboots randomly / slow access to login screen

Hello,

i have some problems with my new DS-7608 NI-I2/8P:

The NVR reboots randomly and is not able to record continous my 4 connected cams. Another point is, that sometimes it takes very long to see the login screen if i try to connect inside my LAN. The time to see the Screen varies from 1s to 30s.

It seems for me the NVR is "busy" with something...does anyone have an idea?

Thanks,
Stefan