Help After update 5.2-5644 Update1 no acces sever

[CKE]

After the update to DSM 5.2-5644 Update 1 via web interface, lost access to the server.

Synology Assistant can not find anything.

after all discs are disconnected and using XPEnoboot_DS3615xs_5.2-5592.1 I do get an IP (as a test)

 

The server boots but it will not connect to the net.

 

Is it possible to downgrade?

Who can help me fix this?

I would like to keep all data.