So much like many of the lockups and problems I used to have with my Garmin Edge 305, even the ugliest of ugliest problems with the Edge 500 has been able to be fixed via the two-finger button combination that hard reset the unit. With the Edge 500, that two button combination is the Power/Light (upper-lefthand corner) and the diagonally across and down Lap/Reset button. From the off state, hold those two together until it powers up and a prompt appears to reset user data. Obviously, try other methods before this because you will have to reset your data screens, you bike profiles, etc. For me, it worked to get my Garmin Edge 500 scrambled data screens back, and again had my abundance of data is available from my handlebars.
Just wanted to share this tip with fellow Garmin Edge users, as my original post about resetting the Edge 305 continue to get a lot of traffic and comments thanking me for posting that tip. Hope this one shows up in Google as well, and helps fellow cyclists.