Deleted all partitions from Mac mini except Boot Camp, now can't reinstall OS X I have a Mac Mini without DVD drive (2010), and I used Boot Camp to install Windows 8.

Everything worked but after I played in Windows with the partitions (I wanted to expand the partition of the Mac). I made mistake and deleted every partition (even Recovery HD) except from my Boot Camp partition. Since then, my Mac mini only boots into Windows. I can't install OS X now.

I took from my friend an OS X Install DVD and Application Install DVD (he also has a Mac mini). Then I took my PC's external USB DVD drive and connected to Mac mini, inserted the OS X install disk and powered on. During the power on I held the ⌘C button and I saw HDD "BOOTCAMP" and CD "OS X INSTALL" so I selected the CD but after that I only see the gray screen with an Apple logo.

How can I install OS X again on my Mac?
Try Internet Recovery. Boot with ⌘⌥R until you get a spinning globe, then follow the instructions.

You'll need to have been fully up-to-date with Firmware updates though.