discovering devices

suggestions: check Windows Disk Manager, check Windows Device Manager, check Windows Event logs, restart BE services, restart the server.  Is the BE server virtual or physical?

If they are stuck against those 2 devcies that are marked with a crossed out pencil (so limited to read operatioons) then bring up the properties of each device and change it so that is is not limited to read operations

Note any disk drive that has been offline for 2 weeks will be marked as read only (unless it is something like RDX and then the default setting is based on 4 weeks) this is by design to avoid data loss if you have removed drives for archiving and then returned then to active for a restore. You can however change the timings etc in the BE settings.