I think I had a similar problem recently. I had a R304SB already bound to my 4PX, & after a ESC/motor change it wouldn't work, no led. I thought the ESC was bad, I was wrong. I had a BN R204GF-E so I switched protocol & everything is fine. I still don't know if the R304SB is any good. I know my post isn't any help, but I'm curious as to what your issue maybe. I would check what above posts state, power & protocol.