Having an issue with VEX robots

[Jay O'Donnell]

Hey CD,
I recently bought a VEX kit and received it a few days ago, but I am currently having some issues and I'm not sure what to do, so I'm hoping that someone can help me. Here's what happened: I put together my first robot, just a simple 2 motor drive train and default code, and it worked completely fine. I then put together a 4 motor drive train and made a modified version of the default code where I changed the part about 2 motor tank to 4 motor tank. For some reason, after I changed to that code only tether mode worked, not wireless. Then I thought I had to do something with the master code, so I downloaded the master code onto the controller. Then I tried downloading that master code onto the cortex and it asked for an access code, which I wasn't sure what to do with. Now the controller won't connect at all to the cortex, and I can't download code at all.
Any help would be greatly appreciated!
-Jay