Hello, I recently purchased a quad core mac pro, and purchased an "insignia" 26 inch TV to use as an "External Monitor".. I brought everything home, set everything up. Everything was working perfectly. Connected the HDMI from the TV too the mac pro. I powered on the TV and the OS was running perfectly, however the display ratio needed to be adjusted. So I went into system prefs and adjusted it too "1800 P" and the screen went black.... I've been trying for an hour to try and get the screen to work again, but the mac wont connect with my TV so I can switch it back.. Is it possible to use my mac book pro ( I'm posting with it now ), as an external monitor so I can readjust my settings back to what they were before? What should I do? Thank you so much for reading!