Canon PowerShot SD400 No memory card message, but there is a memory card installed. Tried multiple memory cards and got the same message. Made sure the memory card was locked.

There are several possible causes for "memory card locked", "memory card error", or "no memory card". Some include trying to use a 4GB SDHC card with an older camera made before SDHC format came out. Others include problems with the tiny slide switch on the side of the card, or the electrical contact switch internal to the camera. The problem may also arise from simple formatting problems if the card has never been formatted in the camera (note that this will also erase the card). Troubleshooting tips for this problem may be found at this link. By the way, if you're using 4GB or larger SDHC cards, they won't work with the SD400 as that camera was made before SDHC came out. Consider 2GB or less standard SD cards only. They're very inexpensive these days on Amazon..