Go under the Apple in the upper left hand corner to "About this Mac". Please give us the operating system information and the amount of RAM. Then go to www.firefox.com and download their browser. Try using that and see if it still shuts down. If if does, then I need you to open it up via the three screws on the bottom of the frame and examine the capacitors (cans) for corrosion and/or bulging (a major issue with this model series). We'll go from there.