What is the front LED indicating? Does it go off or does it remain solid amber for instance??
Tell us the tell-tail signs..
Solid amber is the most common at this stage and means a dead hard disk.
The TC will not finish booting if it finds a dead drive..
Or the LED doesn't come on at all or goes off very quickly which is a bad power supply.. not likely in the Gen4 or shorted board.. preventing the power supply from starting up.. that is highly possible.
Both Gen3 and I suspect Gen4 will suffer from this due to bad batches of ceramic capacitors.
2years old is still under apple care if you have any on a computer.. apple will replace the TC for you.
Fix may be easy enough if it is just a dead drive and you have no applecare.. just pull out the dead disk and replace with a new one.
Blinking amber should be ok.
Try again.. do it in complete isolation from the main network.. plug LAN port on the TC, into a single computer that has wireless turned off.
Factory reset.. power down the TC.
Hold in reset.. and power on the TC.. without releasing reset.. keep holding for about 10sec until the front LED flashes rapidly. Now release reset.
Make sure that the ethernet connectivity LED is on.
On the computer ensure the ethernet gets an IP from the TC.. it should be 10.0.1.2
Now start airport utility.. for this to work if you installed 6.3 utillty you must turn on ipv6 local link on the ethernet connection.. this was belatedly realised by apple.
If you cannot access the TC something is wrong and yes, time to exercise your applecare.. otherwise just setup the TC again.
Tell us how it goes.
this is how i fix my Time capsule.
After i try all method found on internet i order a new one ...my old was 3rd generation and was out of apple care.
I decide to use from this defective the hard drive, and after i remove i put in an external case and surprise....my hard drive was fault. I put in my time capsule a new hard drive and now work perfect...no more "AN UNEXPECTED ERROR' how LaPastenague say,time capsule not boot until chek the hard drive.
So i sugest to check hard drive and try again whiat a new one, that work for me.