iMac Additional Display Issues

[chucknasty]

I've been playing around for the last couple weeks with setting up my home office centred around my iMac. For a while, I was running a Toshiba TV as a secondary display through a mini-DVI to HDMI adapter, which was working perfectly. Since the iMac has only one video output, I ordered a external video converter to set up an additional Samsung LED monitor through a USB port. Now that I am attempting to run a multiple display setup, my Toshiba TV claims that it is receiving no video signal. However, the computer can still detect the display, and I can move my mouse over to where it should be. I tried switching my adapters, ie. the Samsung connected directly to the computer via mini-DVI to VGA adapter, and the TV connected via the external video adapter. This setup works, however it is insufficient for video streaming, which I am dead-set on having on the TV, not the monitor. I switched back to the original setup, but still seeing no video signal. I have switched both the HDMI cable and mini-DVI to HDMI adapter, with no luck. I am quickly running out of ideas and really want to get this setup working. My only other thought is the issue may be related to the driver that was required for the external video converter (Sabrent), the only internal change to the setup since it was working less than two weeks ago. . Please help!