27" iMac with mini display port and Windows 10 - use in target display mode? I have a 27" iMac, with a mini-display port. I do not have MacOS installed on it. Instead I have Windows 10 installed on it. Can I enable target display mode using this configuration?

If not, how could I get into target display mode without removing Windows 10 from the internal hard disk?

Model: Mid 2010 (2.8GHZ QUAD-CORE INTEL CORE I5, ATI RADEON HD 5750)
So for anyone with the same issues. Indeed you need a working copy of MacOS in order to enable Target Display Mode. So using the internet recovery option (Command+R while booting up) I installed MacOS on an external 32GB usb stick attached to my iMac. Then after about an hour of installation the iMac booted into High Sierra and using Command+F2 it switched into Target Display Mode and I was able to use it as a second monitor for my Windows 10 PC.