Casio Exilim camera no longer visible to iMac

Hi, I've downloaded photos from my Casio Exilim camera dozens of times before to this iMac. Today, connecting to the USB port doesn't launch iPhoto, nor does the device show up on desktop. I tried using Image Capture, and got the msg no camera or scanner connected. I've got Mac OSX 10.6.8 with 3.06 GHz Intel Core 2 Duo. What is the fix? Thanks, Nora

The fact that you have done this before is a good thing.

Start by removing the USB cable from both your Mac and the Camera! This is important, 3 separate things.
Check your Camera has a good charge in its battery. Turn it OFF.

Restart Your Mac and Login. Give it a minute to finish load all the background tasks.
Turn your Camera On and into the correct mode. Often called PC mode.
Plug the Cable firmly into the Camera.
Plug Cable firmly into the Mac USB port (not the one on the Keyboard, if it has one).

That normally sorts it, if this doesn't work then try a different cable, try a different Mac to see if the problem follows the Camera.