After successful install, both Windows and Clover stuck as “missing operating system”

I recently installed Sierra on my machine (it’s been installed before successfully, just now putting it on an SSD so I had to reinstall. Install was smooth, but I made a critical mistake, I did not install MultiBeast and Clover before taking the USB stick out. Now cannot boot into either Windows or Mac, and the PC doesn’t recognize my USB disk that I made with UniBeast. All I get is a “missing operating system” error. My entire computer seems completely unusable. Any suggestions or help would be greatly appreciated.