I'm sorry to hear that you're having trouble connecting your PC.
"Mode Not Supported" is usually referring to not having the video card setting set to a compatible resolution. Page 60 of the manual lists all of the supported resolution, and Page 61 gives some information on connecting a PC with the TV's menu.
Also, check that you have the latest video card drivers, and that any overscan setting in the video card is set to 0%. (Some video cards have this, others do not).
Tried to connect my PC and get Mode Not Supported. Connecting via VGA to DLP Model HL-T5676S. Want to use for NetFlix.