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.
Thanks, your excellent detailed post helped me to no end.
I just recently had my Time Capsules internal 1GB drive start to go bad and then luckily before it completely died I backed it up to an external USB 2GB disk.
Strangely when I added the 2GB external drive, got it backed up, then was able to use both drives fine for a few days before the original internal drive died.
The Time Capsule got into a state of working fine for the WiFi and Ethernet connections but neither disk would be accessible. This happened once between adding the new disk and I managed to be lucky and it booted again with both disks then both drives becoming unavailable again. When the disks became unavailable I was also not able to get Airport Utility to talk to the Time Capsule.
Upon rebooting again it became stuck in a state of no completing the boot up until I removed the internal drive.
There were a number of webpages covering drive replacement but none discussing that it would work without an internal drive. iFixIt had this tutorial describing how to remove/replace the drive.
In the end I just removed the disk drive and gave it a go. Airport Utility displayed an error about an internal drive error, but it was easily "ignored" and my Time Capsule is back in place with all settings intact and my external 2TB disk drive.
I'm hoping this will continue working well, and plan to check if I can now recover the disk drive further, but won't rely on Time Capsule for my complete backup backup.
P.S. my Time Capsule seems to be a Gen 2