Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I think the problems with those two Kenwood devices are completely unrelated.
The dnn770 has probably had its firmware update applied incompletely or irregularly. That can make a device suffer a complete failure-to-operate condition, or erratic but constant and persistent failure to work.
The dnn990, on the other hand, may have damaged firmware/software, and/or a severe and basic hardware/electronics failure. That is what usually makes a device restart over and over again repeatedly.
I would advise that you re-apply the software update to the first of these two... if you can.
And that you apply a software update or software refresh to the second one ... if you can.
Otherwise, they will need to go to a Kenwood factory service center for repairs. If it comes to this, please indicate your location (the indications are that you are in Argentina, but I cannot be sure of that yet.) With your location, I can tell you where and how to send the Kenwood devices for repairs.