vga box compatible games don't work with vga cd-boot!!!!!!!!!HELP!!!!PLEASE!!!!

I DON,T UNDERSTAND WHY IF I LOAD VGA CD-BOOT AND THEN REPLACE WITH VGA COMPATIBLE GAME NON-SELF BOOT AS CRAZY TAXI,F 355,ECCO THE D.,V-RALLY 2,REVOLT AND OTHER THE SCREEN SEEM BLACK BUT IF U LOOK FOR SOME SECOND U CAN SEE THAT GAME HAS LOADED BUT SEEM AS BRIGHTNESS HAS GONE DOWN!WHY?I CAN SEE THOSE GAMES ON A PC MONITOR? HOW?PLEASE SOMEBODY HELP ME!!!!!!
EXCUSE FOR MY BAD ENGLISH THANX