I am trying to extend the desktop of the iMac with a Dell 240WFP. It is connected with a Mini Displayport to HDMI adapter to a HDMI cable into a DVI-HDMI adapter plugged into the Dell. The iMac detects the display but the Dell is blank and just keeps flashing "entering power save" intermittently. If go in and change the resolution of the Dell, it seems to "respond" as the message goes away and is replaced by "no DVI-D cable." Do I need a Mini DP to DVI adapter? Any ideas?