ANALOG TO SDI NOT GIVING SIGNAL

My organisation Bought ATEM BLACK MAGIC SWITCHERS and so we bought converters as well to fit in the signals but after some days the converters stopped giving out signals to the output.
Please what can i do to solve this.

Please can someone help me out

Yiu need to post more information, which model STEM, which model converts, what is the video resolution the switcher is set, what type and model of cameras???
DS