Ouch! Bricked my mac...

Somehow I have completely bricked my old Mac Mini Mid 2012.

I was trying to set up a multi boot (windows/linux/osx) and was installing rEFIt. The installation failed with an error and after rebooting the mac will no longer come up. In fact I don't even get the apple logo. I have tried

Alt+Command+R, Alt+Command+R+P, boot the original Mac install DVD. Nothing - only a black screen (I do hear the start chime).

I had macOS Sierra installed at the time - not that it would make much of a difference.

Any suggestions on what to do if you do not even get an Apple logo on boot?

Thanks