Oxygen 3 will not turn on
This is often caused by a failure of a fuse on the Sumo board, or occasionally by a failure of the cord reel. I just posted a rather extensive set of instructions on how to check these things as a response to a different thread, but I will repost them here:
There is a board in the back (called the "SUMO board") which has a fuse hardwired to it. Most of the "no go" problems with this machine are related to this.
In order to check it, you'll want to take a thin flat-head screwdriver, and gently pry up the silver panel on the top of the machine. The easiest place to do this is on the side of the panel, as far toward the rear of the machine as possible.
You will then need to remove the 2 Torx screws on the rear panel, and the top body of the machine should then be able to be removed. There are two clips in the bag chamber, directly under the back portion of the bag compartment lid, which can be pressed in to facilitate removal of the back cover.
The sumo board will be sitting directly on the top of the machine, and the fuse in question will be on the right if you are looking at it from the rear of the machine. Unfortunately, if the fuse is blown, you will have to replace the entire circuit board. (Unless you feel very comfortable with soldering a new fuse onto it, which I do not recommend for safety reasons.)
You can also check continuity of the cord reel from here. On the right hand side of the board are two spade terminals leading to wires running down into the cord reel assembly. One black, one white. Checking the continuity between these terminals and the ends of the power supply cord will allow you to determine if the cord reel is providing power to the machine.
Accessing the cord reel will require you to remove the six Torx screws holding the main body to the base. Two of these are on the rear of the machine, and are very deep inside; so you will require a very long-shanked Torx driver to get at these. Two more are inside the bag chamber at the rear, and the other two are on the front handle assembly. This will allow you to lift the main body away from the base, and if you are replacing the cord reel you can pull the wires from the spade terminals and the socket on the sumo board, and feed them back down into the cord reel chamber to remove the old cord reel.
Reassembly is simply a reverse of the previous. Beware, however: getting the cord reel to align is something of a chore, so make sure that you have the retraction system functioning before you put the whole thing back together, or you'll be bummed when you finish reassembly and the cord won't retract.
(I've definitely never done that. Nope. Never.)
Hope that helps, good luck.