my time machine no longer appears in airport utility "No configured AirPort base stations have been found."

Basic troubleshooting: start with a "hard reset" - hold its reset button depressed continuously, about five seconds, until your TC's LED flashes rapidly. After a moment or two it will flash amber, slowly. You will then need to reconfigure it using AirPort Utility.

This does not affect your Time Machine backups.

If its LED remains illuminated amber without blinking after several minutes, it may have a problem you will be unable to fix. In that event, try another "hard reset".