Replacing the Internal Time Capsule Hard Drive
You need to let the TC format the drive. If you can't make that happen using a reset + reconfigure from the AirPort utility, you might have an incompatible drive (i.e. Needs more power or cannot be used due to incompatible features).

It's not going to work like an external drive that happens to be built in, the TC OS needs to manage the disk. OS X can read such disks, so it might seem like any normal formatted disk if you hooked up the old one.

If you still have the old drive, you might have more luck cloning it to the new one prior to installing it. 

Also, if wifi doesn't work, ethernet might still work, especially if the Time Capsule needs a reset.