The rumba shows up as Com10. But neither Simplfy3D or Repetier Host can connect to com10 when selected. I'm resorting to sd card printing which is cumbersome.
As @Rob Heinzonly says. Check your baud rate. Marlin on Bigbox has been changed to 230400 as default. This is because Linux/Mac do not like 250000.
Hehe, I learned that the hard way. Was running on a Ubuntu machine and could never connect to a RAMPS board until I changed to 230400.