I'm assuming you mean the Linkstation ls410d, if not please correct me.
You can remove the drive from the device and connect it to a PC to recover the data and run diagnostics on the drive (hire a professional to do this if the data is sufficiently important). It's somewhat easier for the single-drive models because you don't have to worry about software raid.
You can:
remove the drive from the device
connect the drive to a pc either via usb adapter or directly
boot into a Linux live environment
mount the data partition and backup data as needed.
look at SMART data/run diagnostics to determine if the drive is failing.
I've got notes and pictures for how to take this device apart (it only requires one screw from behind the sticker on the bottom):
https://buffalonas.miraheze.org/wiki/Linkstation_LS410DIf you want to replace teh drive with a new one you can load the firmware with this procedure:
https://buffalonas.miraheze.org/wiki/Restoring_Stock_Firmware_without_TFTP