Resetting PRAM and NVRAM

1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

To take a picture of the whole screen, press Command-Shift-3.
To take a picture of part of the screen, press Command-Shift-4 and drag to select the area you want.
The picture is saved as a TIFF file on your Desktop. Note: Mac OS X 10.2 and later saves pictures as PDF files.
To copy the screen capture to the Clipboard instead of saving it as a file, press Control-Command-Shift-3 to copy the entire screen to the Clipboard, or Control-Command-Shift-4 to copy the selected range to the Clipboard.

Change Screen Capture Format:
Run Terminal Command ->
defaults write com.apple.screencapture type jpg
Logout Or Restart

Support Format:
JPG/GIF/PNG/PDF