Card locked please help

Hello,
There are two reasons for card locked problem Canon PowerShot A400.
One is card locked while camera opening. The answer for this is explained in below figure.

The other one is dealing with card itself. The below picture shows that.

You may need the user manual for other problems.
This is User Manual of Canon PowerShot A400

If you find this helpful please vote.

This is usually caused by the SD card, and is nothing to do with the camera. On the SD card there is a small slider - which allows you to lock the card (to prevent accidental erasure).

If you put in on the table with contacts upwards, corner cut top left, then the slider is on the right hand edge, about 1/3 the way down. If it is slid to the top position (nearest the contacts) the card is unlocked. If it is slid down (away from the contacts) the card is locked.

If it is a damaged / "cheap" card, sometimes the slider falls out, in which case the card is locked. You can still read from it, but not write to it until fixed or replaced.

First check is to turn the camera off, remove the card, move the slider to locked, then back to unlocked. Replace in the camera and turn on.

Have you tried the camera with another SD card, to see if the problem persists? (A reputable photo store will often lend you a card for the 20 seconds it takes to do this test)