When i try to take a picture it says "no memory card" I have tried several different memory cards and made sure they were all "unlocked"

in camera memory is alredy full but u say only memory card formaat pls look the camera memory and no answer that the card is full

There are several possible causes for "memory card locked", "memory card error", or "no memory card". The most common cause is having the tiny slide switch on the side of the card in the wrong position. There are also other common causes if the above didn't help, with troubleshooting steps for this problem listed here.

Gary, I'm guessing that you just bought a new 4GB SDHC card. You do understand that your camera model can only use 2GB or less standard SD card (still available on Amazon)? Please see this link.

Look at the memory card. SD cards have a slide switch along one edge. The position farthest from the contacts locks the card, protecting it from writes. The position nearest the contacts unlocks the card. If the switch is already in the proper position, slide it fully the other way and then back again.

If that doesn't work, try another card.

This camera will only handle a 16GB capacity flash card the camera Firmware will not allow for larger cards. I ran into a similar problem (different camera) but solved the dilemma with updating the camera firmware. I can only suggest you check out your camera model on the Sony web site for updates if you purchase Memory Cards larger then 16GB. If you have cards under 16GB check make sure your camera is set for memory card and not reading from the Internal memory. Another crazy thing is make sure your clock is working (day date & time) and set correctly.

Okay, you put your pictures on the computer hard drive but, the pictures will still be on the card until you format the memory card in the camera. So then you loaded the pictures back on the card so in fact you have two sets of the same pictures on the memory card maxing out the cared capacity. I doubt they will show on the camera because there will be different file formats one from the camera and another from the computer. So to clean things up first make sure you have your pictures on the computer hard drive then safely remove hardware or eject the camera memory card and unplug the cable. then go into your camera settings looking for "Format" might also say initialize but format is pretty well universal anyway find format and follow the screen. Formatting cleans off the memory card and reformat the card back to new to receive more pictures.

Make sure that you are using 2GB or less memory cards for your older camera. 4GB or higher SDHC will not work with an SD300. There are several possible causes for "memory card locked", "memory card error", or "no memory card". Some include trying to use of 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.

The actual memory chip from the card has failed. This is unrecoverable and unfixable - the card is dead, get a new one.

First make sure that the photos are not actually on the camera's internal memory and not shot on the card to start with. Do this by trying to look at the photos through the camera with the card out of the card slot. Next before taking anymore pictures try putting the card into a different computer and card reader. If it still shows up empty you can try several recovery softwares online for free, only paying for them after they have found your photos and are ready for saving. If that doesn't work if you have a local photo store still they will offer recovery service and recovery services are available from companies like DriveSavers.com. Be warned, it can be expensive.