Wrong settings?

I have a Nikon D40 and when I take photos, half of the time the photo will turn out fine, but the other half it's too light and ends up white. I have all the original settings that the camera came with, and I can't think of anything I can do. I'm not sure if it's something that i'm doing wrong, or if it's a fault with the camera. Any help much appreciated! Thank you.

It will help if you post an example....preferably from your computer so we can see the exif data.

What original settings are they? Are you using the auto mode? whats ISO/metering mode?

Are you using an external flash? I have the D40 and I have an external flash that causes errors from time to time, including all-white exposures. A defective flash will screw up the metering which can cause all white (or all black) exposures, since the camera thinks the flash is going to fire (or not fire) and it does (or doesn't).

If not, what camera mode are you in? Are you in Auto or are you in one of the program (S, P, A) or manual (M) modes? If in a program or manual mode, you may have accidentally set the aperture/shutter incorrectly by turning the thumb wheel.

Did you change exposure compensation? When you look at the LCD screen and it shows the camera settings, are they all 0.0 or are there any that have a + or - number instead?

Finally, are you using the kit (18-55) lens or a different lens? If you remove the lens and then re-attach it, does that clear the error? Could be a bad connection.

what r they on right now? or can u show us examples of the pictures?