Hard drives suddenly not mounting

[Xeep]

I have OSX installed on an internal SSD. In addition I have 2 other internal SATA drives and an external USB drive. I went to use my computer today and the only drive that mounts is the primary SSD. Disk Utility shows my external drive but if I try to mount it I get "Count not mount "disk2s2". (com.apple.DiskManagement.disenter error-119930868. The other drives don't appear at all. Additionally, it takes the computer at least 10 times as long to boot up now. Any ideas what might have happened. I hadn't done anything at all to the computer.

 

[P1LGRIM]

Classic symptoms of a dying drive.

Disconnect all of the other drives except for the one that contains the OS.
If it boots normally then shut down and connect one more drive and try again.
If it does not boot normally you have found your problem drive.