No bootable device - Insert boot disk and press any key

Hi! I own a mac mini late 2012. I tried to install with bootcamp windows 10. Everything went smoothly until i had to choose the option Windows home, Pro, Education etc. On the next step I couldn't install it, so I pressed the X button to close it. Since then, every time I open my mac mini it's a black screen saying No bootable device -- insert boot disk and press any key. It just doesn't respond. Any help?