ReadyNAS NV+ blinking power light

I'd begin by testing the disks in Windows PC using the vendor tools - seatools for seagate, and lifeguard for western digital.  I wouldn't allow either tool to "repair" the disks, as that might get in the way of data recovery.  The goal instead is to sort out the disk health.

The most conservative approach is to clone the disks to new ones before attempting recovery.  This would be done with a utility that does sector-by-sector cloning.  There are several free utilities that will do this, including Clonezilla.  If you don't clone the disks, then you should be very careful on allowing more writes to the data volume - that could make recovery more difficult.  In particular, you should use the boot menu option to skip file system checks if you boot the NAS again.

Other options are 

• Engage Netgear Paid Support.  You might not need recovery, your issue might be a problem with the OS partition, and not the data volume.  Netgear could sort that out, and they do offer data recovery if that is needed.
• get a software package for data recovery (R-studio perhaps), and get whatever you need to connect your disks to a Windows PC.
• Boot up in tech support mode, and attempt more troubleshooting on your own.

IMO the last option only makes sense if you already have some familiarity with linux commands.