Logitech K120 Wired Keyboard for Windows, USB Plug-and-Play, Full-Size, Spill-Resistant, Curved Space Bar, Compatible with PC, Laptop - Black

Get a wired keyboard and mouse and try using them for setup. If you wiped everything you probably wiped Bluetooth pairing so the Imac isn't recognizing them and won't recognize them until you're logged in. If you don't already have these devices and can't borrow them get the cheapest Logitech versions that you can get are fine. Amazon carries wired keyboard and mouse or set that you can get. An optical mouse is nice too. If you've not used the Apple KB and mouse before you may find that you prefer the PC version anyway.