Hi Ronil Jogia,
a. Are you facing this issue from the day one you are using windows 7?
b. Did you make any changes to your computer recently?
c. Are you getting any error messages?
Random shut down may be because of many reasons like hardware failure, driver issue or software issue.
I would suggest you to disable Automatic Restart on System Failure and check for error messages. Post back with the exact error message so that we can help you better.
Steps to Disable Automatic Restart on System Failure:
1. Restart your computer and start pressing the F8 key on your keyboard. On a computer that is configured for booting to multiple operating systems, you can press the F8 key when the Boot Menu appears.
2. Use the arrow keys to choose Disable Automatic Restart on System Failure in Windows Advanced Options menu appears, and then press ENTER.
Hope this information is helpful.
Umesh P - Microsoft Support