I have a Nikon D90 and many times it won't take pictures when I press the shutter. Anyone know how to fix it?

B"H These cameras are built with a brain, if the camera think that according to your settings the exposure or focus are incorrect then the camera will not take the picture. So, make sure always to look at the numbers the camera is showing you in the viewfinder to make sure they fit the situation and stability of the picture. Also, if you have a lens with an Aperture ring make sure it is locked on the highest f-stop. Use only high level SD card and not a cheep one, it could send the camera confusing signals. Otherwise, take it to the store for checking.

Your focus may not be fixed; the shutter won't release unless it is. If you're sure that's not the problem, you should contact the reseller and ask for an RMA (Returned Merchandise Authorization); they'll either have it serviced, or replace it. The problem won't get any better, so the sooner you get it serviced, the better...

My D90 has exhibited the same problem. Like noted above, the 'smart' camera has decided that the picture, focus or light, isn't any good. Two suggestions: 1) make the camera happy by getting the focus or light right, BTW I use AF-A. 2) rotate the selector to 'M' and take control of your camera.

Another thing the D90 is known for is a bad connection between the lens and the camera. This is especially true with the 18-105mm kit lens. The camera will not take a pic until you jiggle or re-seat the lens.