Funcation File Problems

I hope someone can shed some light on this for me, I don’t know if it’s my server or what. But when I’m custom designing a theme or need/want to add something to my functions.php file normally the site goes haywire. By when you try to load the page it’s just blank and won’t load anything, or the same thing happens when you try to access the admin panel. Most of the time I have to use the default function file, which works fine, but if I add any function to that file that’s when the problems start.

I know it’s the function file because I either re upload the a version with the changes undone or change the name of the function to something like function1.php and everything works fine again.

Any one had a problem like this or know the reason why it’s happen or most important have a work around?