I had this happen to me and I called in to ETC support. They had me reset the RAM and it worked great and has ever since.
Three beeps usually indicates a RAM failure (as noted by lidgett) but could also indicate a failure in the graphics card as well. I would recommend opening the console with the power off and reseating both of those components. We have a support article and a TechServ Underground video that shows how to open and perform basic maintenance: https://support.etcconnect.com/ETC/Consoles/Congo%2F%2FCobalt/Congo_Jr./How_to_Open_a_Congo_Jr