Not spinning is a sign of insufficient power, or a failed power controller inside the drive. Having four fail that way is highly unlikely, but possible. You haven't given your location, but if your mains power is erratic, you might be helped by putting a Uninterruptible Power Supply (battery backup) between the mains and the drives. Another way to see if they are spinning is to try to turn or rotate the case. You should feel the gyroscopic effect called precession as you do that. The drive will try to move 90 degrees to your movement. If it does, it's spinning. If not, that's another confirmation that it isn't.
One more thought: I had problems with one drive because the power supply provided by Seagate was barely adequate for the demand. It failed. I complained to Seagate and they sent another, which also failed. I got a third party power supply with twice the power rating and it worked fine after that. You might see if you have a compatible power supply with a higher power rating available to try on the dead drives. Keep the voltage out the same, but look for higher Amps rating.