ColecoVision consoles are notorious for failure, so your situation is not surprising...I don't know what you mean when you say the system gets power, etc., because the CV console lacks an LED. It could be the power switch, but the fact that you are getting only a black screen is not a good sign. Usually if the switch is failing, the system will power up, but will have scrambled graphics. CV consoles are notorious for problems with both the power switch and the power supply (they tend to fail over time), but there may be a problem with the circuit board itself. It could be any number of things, unfortunately.
For a cleaning and repair guide (and lots of other info on everything ColecoVision), try here:
http://www.coleconation.com/
http://www.colecoworld.com/
If you end up needing a CV repair or new power supply, try here:
http://www.geocities.com/double_down_on_11...VideoGames.html
http://coleco.freeservers.com/