There is still no such animal, technically, as a pc cable.
And we do need to know for sure it is DVI and not VGA. If you don't know, look at the packaging again and is the cable called a VGA to HDMI or (1) DVI to HDMI.
If you had some idiotic salesman sell you a vga to hdmi cable, know this: it will not work. VGA will require a converter box to convert the analog signal to digital.
There is nothing you need to do on your Mac. Again, my best guess is that you have not changed the input on the TV, (2) by picking up the Toshiba remote and pushing the 'Input' button until it changes to the input that matches the one you have connected the Mac to.
There is nothing else I can help you with until you verify these 2 items.