Target display mode - hdmi to mini display port

Hi,

I want to use my imac 27 late 2009 as target display for my pc.

I have an HDMI to mini display port cable, which I'm trying to use for target display mode.

For some reason I can't activate target display mode by the shortcut cmd-f2. I don't know if it's the shortcut that is set up right or my cable.

Br,

Sonni