Asustor NAS with unaccessible Volume1

Hey guys, I have an ASUSTOR NAS with currently 3x 4TB WD RED HDDs inside and yesterday oneof them gave a failure so I disconnected and connected it back again (this has happened in the past once and fixed the issue) but yesterday it made the disk not accessible so I rebooted the NAS. When it came back online the volume1 of RAID5 was unaccessible and it has been like that since. Any help?
Thank you in advance!