All of a sudden yesterday my camera kept saying "No card in camera". I worked with it and finally I took the SD card out of the camera and switched it to lock, place it back in the camera and of course got the message that the "writing was protected", so I took it back out of the camera and switched it back to unlock and magically the camera recognized it fine. So, this morning same thing exactly. Question is this, is it the camera, the SD card or both? Please help, this is my work camera and I use it on a daily basis.
It's most probable that the card has simply failed. Another likely possibility is that the contacts inside the camera need to be cleaned.
The first diagnostic step is to try another card, and if possible, to also try the card you have in another camera.
If the card doesn't work in another camera, and if another card works just fine in your main one, don't lose any sleep — just throw it out and get another. (After, of course, copying any photos off the card that you can — see this question if you have trouble reading the card on a computer.)
If it's the camera, particularly since you use this for work, I suggest a professional repair/cleaning. You might be able to DIY this, but I personally wouldn't consider it worth the hassle.
As mattdm said it's best to try another card, another camera (if you have one) and another card reader if that's possible. Another hack I've done is put some tape on the "lock" of the SD card so that it reads correctly.
If not you can read my related post, Nikkon DSLR messing up SD Cards
I haven't had a card die on me unless it's really old, a few years a least so that might be your other problem. SD cards don't last forever, and their contents can degrade but it doesn't mean they can't be used.