Have you checked all the cabling? If you're using an accel card along with the core card in your computer, be aware that the Flex cable that jumpers between the two cards can fail... this can cause this problem. Also, be aware that the short jumper cables (Digilink 1') between the 192s can also fail, and does quitye frequently. I have had a couple of those fail on me.
Have you tried running the main 192 alone from the computer and then running just the other 192 from the computer? If you try this and they work independently, then one of the cables (Flex or Digilink) is your problem.
If you have done all this, and you most likely have, Next try removing each one of the converter cards in the problematic 192 until you eliminate the possibility that it may just be a failed card. 192s come standard with 8 in and 8 out (one DA and one AD card each) and the third and fourth cards are usually installed afterwards (either at time of order placement, at the dealer or as an upgrade). It is not uncommon for one of these cards to fail.
The idea of the entire unit going down is a possibility but not what usually happens.
I hope I have been helpful to you, if not, perhaps this post will serve to help someone else in the future.
Kindest regards, and may the odds always be in your favor.
Free the electrons! Use tubes/valves when possible.