How to reinitialize i-mac 2007 OS X 10.4
Internet Recovery isn't going to be programmed into that old of a Mac. Similarly the recovery HD isn't available with OS older than Lion.

You need to boot from the 10.4 installer or bring another bootable volume with MacOS on it to that Mac to work on it.

I suppose what "intiailize" means to you will govern if single user mode is of any help at all.