I was at a basketball game last night and taking pictures with the d80 and the 55-200 lens. All of the pictures I took in auto focus were blurry. I changed it to the S mode with shutter speed at 4000 and those pictures came out completely dark with nothing in the picture. I changed the setting to the sports mode and the shutter speed is not fast enough because I have the same issue with blurring or out of focus.

Go to MENU. Then TOOLS. Make sure Motion Detection is in AUTO.
If that is on AUTO then Put the camera on a hard surface (like tripod) and focus and see if image is still blurry. Lastly, it is difficult to focus in some conditions. Move the focus point, you can click on the screen to change it. Blur can be caused by: long exposures, camera motion during photograph, bad conditions unable to focus.

The focus routine in this camera gets confused often. It can be frustration. It will only be in focus when it is GREEN before you shoot and the camera is not shaking. At night it can take great night shots with a TRIPOD and Exposure set to -1 to -2.

Make sure your lens and any other small sight glass areas on the front of your camera. Some of these lenses are for the auto focus and may not work if dirty.

You did not say which lens or lenses you are using, but most auto-focus lenses have a switch for selecting manual or auto-focus. First, check your camera's menu settings to make sure auto-focus is enabled and then your lens to make sure you did not accidently leave it in the manual focus position? If it is in the auto-focus position and still not taking sharp pictures, switch it to manual and see if you can get it to focus correctly. It is also possible that your auto-focus alignment is out because your camera was bumped, jolted or dropped. If realignment is necessary, you can send the camera and lens to Nikon for repair or find a knowledgeable camera repairman.

Clean the contacts on the camera body and the lens where they meet with a cotton swab dampened lightly with rubbing alcohol.

You could have cracked the lens, damage the focus or a number of other things but the lens and focus are most likely. check your lens for scratches if there is none and no cracks take it to your nearest camera store or buy new good luck!

That's a big lens and for sports photography you are going to need a lot of light to ensure you can use a fast shutter speed to capture the action. Sports mode may do too much for you and you might want to try switching to a more manual mode. Try switching to Tv mode which gives shutter speed priority. Set the shutter speed to something around 1/150 or higher (1/200) which should be fast enough to freeze the action. Make sure the ISO is set to 200 or 400 for best results and see how you get on. This should stop any action based blur which would leave you with focus problems if the pictures are still blurry. Check out http://www.dpreview.com/reviews/canoneos450d for info on what this camera can really do for you

Have you tried a different lens on the camera almost any lens with the same mm size will work. If it still does not take pictures with another lens. You should take it in for service.

google its user manual

changing lens from stock might be the issue
or 8 years auto focus sensor may be stuffed

I have had to replace the focusing servo motor is these before. The problem of seeking without locking in may mean the same for your lens. Do check for a dirty filter on the front and look to see if the rear optic is dirty or cloudy first. I'm assuming other lenses work fine on your camera.

You probably got some condensation on the lens from going in and outside. You should be able to go to a Wolf Camera or similar store and have it cleaned.