This does not sound correct. Can you post a screen shot?
Command-Shift-3 takes the entire screen
Command-Shift-4 takes a portion of the screen. <--use this one
Use the camera icon to upload the image.
Start by running Repair Permissions in Disk Utility then restart in Safe boot mode and see if these simple steps help.
To use Repair Permissions:
1. Open Disk Utility in your Applications/Utility folder.
2. Click on the First Aid tab and select Repair Permissions
3. Click on the icon for your boot volume.
4. Click the repair permissions button.
Safe boot
* shutdown
* start the Mac and *wait* for the startup chime to sound
* after the sound, press and hold down the shift key
* keep holding and *wait* until the grey Apple logo appears
* now release the shift key and just wait (it could take a few minutes)
* eventually the login screen appears with the words SAFE BOOT
After logging into your User, do you still see the problem?
If yes, testing in a new User will quickly tell you if the problem is system wide or if it's your User's folder that contains the problem.
CREATE A NEW USER
Go to System Preferences --> Create a New User in Accounts. Switch to the New User by logging out/in or use Fast User Switching.
Do you still see the issue?
If yes, then the problem is with your base files.
If no, then the problem is in your User's folder.