My question is regarding the Airport Time Capsule. I can see the Capsule via AirPort Utility but have no access to its hard disk. Please, help.

Would help if we understood what changes that you made on your home network. Can you please provide some details?

When you could access the Time Capsule hard drive before, what steps were you using to do this?

Have you updated the operating system recently on the Mac you were using to access the Time Capsule hard drive?

Power off all devices on the network.....modem, computers, printers, iPhones, etc.....in any order that you want.

Wait a minute

Start up the modem and let it run for a minute all by itself

Then start up the next device connected to the modem and let it run for a minute

Keep starting up devices one at a time about a minute apart until the entire network is powered back up

If still no luck, you will need to reset the Time Capsule back to its factory default settings and then set it up again. You can use the same name and passwords that you used before if you wish

Have you powered off the entire network......all devices......waited a minute, then started up each device one at a time starting with the modem?