2 things to try when hooked to the external monitor and the signal goes off did you hit FN
+ F5 to see if it would switch screens? If you shine a flashlight across the screen from side to side can you see an image?
There are issues with Nvidia Laptop GPU's HP and Dell have extended warranties for an additional year(Like you only expected the laptop to last 2 years) but so far Toshiba has not, that I know of but it's worth a call.
http://news.cnet.com/8301-13554_3-10020782-33.html