under lite-c you do define and initialize the variable...

var video_mode = 8;

...also make sure you are not switching to a higher resolution than you are using on your desktop....I think this used to be an issue. I'm sure you support this resolution though.
One more thing is the wait instruction...use a while(1) tester if you are using wait(1) but place you variables before it...

fuction main()
{
var video_mode = 8;
while(1)
{
wait(1);
)
)