N4100 Raid 5 dissappeard after 2 years of running

Hello to all

Since yesterday i has some troubles with my N4100. From one moment to the other my raid 5 with 4 x 500GB harddisks is disappears.

I do no updates or somthing else. Did any know somthing about this troubles. In the status display all informations about Raid are N/A. What's happen there? Disk status is ok for all 4 Disks. Does anyone know how to fix this troubles. Schould i rebuild the Raid? I dont want to loose my datas! I downloades my conf.bin. Schould i upload my old conf.bin to restore the Raid5?

Over Nettwork its not possible to access the nas. i has no possibillity to mount the drive. I had some special messages in log like: 02:31:29 disk 3 on is removed an next log entry is 02:31:31 disk 3 on is inserted. whats the meanning of that? i dont remove any disk! Is a Disk broken? Status for all Disks is ok!
Please help.

Regards from Zurich

Spin