Window size

My game has the following code:

At the beginning of the game
video_mode = 8; // 1024 x 768
video_window(NULL, NULL, 4, "CMS Systems 1.0");
Then I added 2 functions that are called from buttons:

function set_full_screen()
{
full_screen=1;
video_switch(0,0,1); // full screen
// video_screen=1;
}

and

function set_window_screen()
{
full_screen=0;
video_switch(0,0,2); // Window screen
// video_screen = 2;
video_window(NULL, NULL, 4, "CMS Systems 1.0"); // Windows caption
}

That works well until my monitor resolion is higher than 1280 X 1024. If I set my monitor resolution to 1440 x 900 or 1680x1050 the game window seems to cut part of the game off and the full screen no longer works.

Any suggestions?

Thanks for helping
Gerrit