Boot camp with windows 7 didn't work, and now i can't boot into OS X

I have an iMac from late 2012 running OS X 10.8, and this morning I used boot camp assistant to install Windows 7. When it booted off the windows partition, I got to the language select screen, but the keyboard and mouse (made for windows 10, wireless and connected using the same USB), input wasn't working at all. When I powered off and turned the mac back on, it only got to a black screen saying 'No bootable device -- insert boot disk and press any key'. Holding option, command + r, shift + command + r, or any other keybind did nothing while powering on, and I have no way to get back to OS X. Does anyone have any suggestions?