I bought a canon sd1100 a year ago. It used to take great pictures. One month ago all pictures taken have been grainy. Do you know why>?

If you bought it new a few months ago take it back for a repair under guarantee

Hello, Cameras today are all rated as mega pixels. The higher the (MP) the more detailed a photo will be. Vivitars' higher end cameras are great, but their entry-level ones aren't. Sometimes when purchasing a budget camera, you may notice that the built in lcd (for preview) looks really grainy. This is because the manufacturer uses a cheap lcd display to keep the costs down. Now if the digital picture itself is grainy, then it's time to return that camera. I don't want to just blurt out a camera model to you because I do not know the age of your child and at what level of responsibility she has with fragile electronics. But generally speaking, Canon cameras are amongst the best. Whether it's an entry level model or a high-end model, these cameras are fantastic. Again, the image produced is rated by its MP.....anything over 3MP (which most cameras are currently) and you will be taking high quality shots. Honestly, I would look into Canon and pick one that is sleek and maybe her favorite color. You CANNOT go wrong with them, unless she breaks it. =) I bought one for my sister, one for my dad, and one for myself and am so happy with it. Sony has nice cameras too in this price range but did not have the same ergonomics features (to me). The best thing to do is stop by a BestBuy and play around with a few cameras. I hope you see what I mean when you hold a Canon in your hands. To be realistic, you should spend around $140-$200 max. I bought myself a Canon SD600 years ago, with I believe 6MP(which is pretty outdated) and I absolutely love it.
My advice to you is however cheap the camera, get her a Canon. =) Hope this helps.

Go to the menu and look for "Reset Default" and that will reset your camera to the way it was. See if that brings the quality back ..

the problem must be because of the resolution dpi value. it does not matter if your image is BIG and looks great on your comp, but if the dpi value (which can be found by Image->properties thru the right-click option) is lower than say 300, the image won't look good on print.

A stuck shutter is another common failure mode for digital cameras. The symptoms of a stuck or "sticky" shutter are very similar to CCD image sensor failure. The camera may take black pictures (for shutter stuck closed), or the pictures may be very bright and overexposed, especially when taken outdoors (for shutter stuck open).

To confirm a stuck shutter, put the camera in any mode other than "Auto", and turn the flash OFF (you don't want to blind yourself for the next step). Next look down the lens and take a picture. You should see a tiny flicker in the center of the lens as the shutter opens and closes. If no movement is seen, then you likely have a stuck shutter. If so, please see the following for further info and a simple fix that may help:

http://camerarepair.blogspot.com/2009/05/simple-fix-for-stuck-shutter.html

This sounds like it might be a defective CCD imager. If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status. Please check the following two links for more info:
　
http://camerarepair.blogspot.com/2007/11/canon-digital-cameras-showing-black.html
　
http://www.usa.canon.com/consumer/controller?act=PgComSmModDisplayAct&fcategoryid=225&modelid=13390&keycode=2112&id=29819

Applicable cameras include:
A40, A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S200, S230, S330, S400, S410, S500, SD100, SD110, IXUS V2/300/400/430/500, IXY Digital 200a/300a/400/450/500

The grainy effect has to do do with the ISO setting, try adjusting that. A higher ISO is generally better for darker conditions. I have noticed that this camera frequently takes grainy images.

Hmmm...... there might be a time battery that needs replacing. Look fore something like CR1220 or time battery. Pry it open and replace it with a battery of the same size.

It sounds like the aperture is getting set very high. If the aperture is a high number, the lens opening is very small which lets less light in and would cause a dark image. This would also show any dust that is in or on the lens or image sensor. The dust doesn't usually show on apertures with a larger opening (smaller number). Make sure your aperture is being set to a reasonable number, probably no higher than 8 or so.

Are you in night mode? Sounds like you are in a high gain setting, like ISO 3200 or night mode.