I'm having the same issue. As soon as I connect it to VGA or HDMI, it goes into a cycle of flashing on-and-off. A guy on youtube had the same problem (posted a video identical to my problem) and reportedly fixed it with a firmware update.
The problem: the US website doesn't have a firmware download. The canadian website does, but the update is from 4/2009, and the manufactured date on the back of my TV is 5/2009. (I also tried the update, but it didn't fix the problem).
When I call Toshiba to ask about the firmware update, after they confirm I am out of warranty, their automated system keeps hanging up on me. So frustrating.