Flashing Blue Light

First, let's see if it's the hardware or software causing the issue.  I assume you have tried to reboot and got nowhere.  For the next step, power down, remove the drives (labeling the slots they came from) and power up with no drives.  Does RAIDar show the NAS with a "No disks" status?

If not, it's not a good sign.  If you can see it, power down and put the drives back in, then power up to the boot menu and try an OS install.  If you did not see it in RAIDar with no drives installed, a USB recovery might help, but it's probably a hardware problem.

If you can't get to the boot menu with your original array installed, remove all the drives with power off and put in just one drive that is not part of your array.  See if that works, either without intervention or via the boot menu.  If it works this way, you probably have one drive that is so messed up it's bringing down the whole NAS.

If it''s a drive that looks like it could be the peoblem, then use manufacturers tools (e.g. SeaTools) to check the drives.  If one is bad, return just the others to the NAS with power off and see if it now boots properly.

This is a long list.  If you get lost or unexpected results at any point, come back and give an update.  We'll see if we can help get you back on the road.