So I did a cycle guitar recording. Chose the best. Bounced to new track checking box to mute original track. Now I want to work back in the original cycle recording but it won't un-mute. Whats the trick?

Assuming you Cycle-recorded into a Take folder and used "Bounce Regions in Place", then to un-mute the track with the Take folder you need to select the top Region (the Comp Region) and hit Control-M to un-mute it. Apparently when you "Bounce Regions in Place" Logic mutes the source Region, not the source Track. Btw, AFAIK Control-M is still the default key command for Mute/Unmute Region, but if it doesn't work just check the Key Commands window..