Is the TC light blinking? If not and it remains solid amber, you have an issue.. most likely a dead hard disk.
What generation TC ?? What size hdd?
If you are using wireless, disconnect the TC and plug directly into the computer by ethernet.
If you are already on ethernet.. just restart the TC..
If the utility cannot find the TC.. press and hold the reset for 10sec..
So you have a computer.. TC plugged in by ethernet.. no other network connection to TC or computer.
Hold in reset.. if still no TC.. it is dead.. sorry.
Put your ear to the box and both listen for disk spin up, feel the vibration of the spin up, and watch the TC light.
It should at power on.. flash green for a couple of seconds.. you might hear a very faint sound.. the fan starts, then about 10sec later the fan stops. (never to restart. which is a wonder).
Front LED is solid amber for around 15sec.. boot loader and firmware loading.
Front LED begins flashing amber and the hard disk spins up..
You will hear the whine of the startup and the vibration.. the disk should spin up once.. stabilise and click softly as the head locates the start track. It should then spin continously with no change in noise for about 1min and then without activity spin down.
Check the airport utility if it discovered the TC..
If no go.. the disk is busted.
If the LED goes out the power supply is dead.
If the disk spins and the LED is blinking.. you have a Gen 3 with a dead board.
They are the majority of failures.