The manual says that I can use the built-in flash in intelligent auto mode, but when I pop it up it stays off. When I go to the menu, flash is grayed out and I can't do anything with it there. I have tried everything I can think of. Any suggestions??
In short, this mode tends to assume you do not want to take flash photos, but use the flash only as fill light such as when there is strong backlight and you need to see a darker subject in front.
The mode is "intelligent" in the sense that it doesn't just use simple arithmetic to determine what settings to use and whether to use flash, but tries to analyze the content of the live image data it's getting to see what you are photographing and make decisions based on that.
Thus this mode only uses flash when it believes it will enhance picture quality.
If the flash doesn't fire, but the picture looks OK, then there is no problem and it's working as intended.
If the flash doesn't fire, but the picture exposure was too long causing blur, you need to choose a different mode where you have full control over whether the flash is on or off and you can force it on.