My nikon d90 won't let me take pictures anymore?

It keeps giving me an "F" every time I try can someone help?

If the lcd screens reads "Fee), then you don't have the aperture ring rotated to the smallest aperture and locked.
http://support.nikonusa.com/..._id/116678

In the D90 (I have the same camera), F-- means there's no lens attached (or no lens it can detect).

If you put the camera into manual (M on the mode dial), you should be able to take a photo. If you can, nothing is broken.

Remove the lens, then re-attach it. Sometimes the contacts get dirty and this usually fixes the problem.

And if the lens has a manual aperture ring as George suggests, make sure it is rotated to the smallest aperture (f/22 or whatever the largest number is).