Dell 8500 lap top with slow vidio display?

When i down load a radar loop from the national weather service the vidio runs slow and jerky until i hit the "function"+F8 (CRT/LCD) key. The screen will blank for a second and then the display will play at a normal speed. This will stay this way untill the radar refreshes or you leave the site and return. What is the function of the crt/lcd key and can i make it stay in the fast display mode all the time. Thanks.