iMac black screen when Target Display Mode is ended by a sleep.

Hi guys,

I'm getting a really annoying bug happen to me on my iMac (specs below). When I put my PC, which is connected to my iMac via TargetDisplayMode, to sleep, my iMac display doesn't come back on, it just stays black. I can hear the hard drive working but it's completely unresponsive. The only way to fix this is to hold the power button which is not nice if I have work open. This happens nearly everytime and it's very frustrating. I've done the normal checks in Disk Utility and everything seems fine, so does anyone know why this is happening? For the record, I've had very similar symptoms to this when I used to get a black screen after waking up the iMac from sleep, but I identified the problem as Photoshop and haven't had the issue since I stopped leaving PS open.

Thanks for the help,

Mike