I put this line onto function WINDOW MAINSTART {} : BG_PATTERN <myflash.pcx>,...
or somethings like this .But I had an error dialog when I published my games, it says : No started definitions found.How do I fix it. Please help me ! Thanks in advance.

You need the Pro Edition from GS to use WINSTART.

Sure, I'm using the Pro Edition, but i can't put an image onto startup screen.