If you have a computer which works fine and without any issues and suddenly you find it locks up, rebooting itself and shutting down with no reason, then you know what is wrong and hence you need to follow the simple steps;

1. Check for recently installed software or hardware- If the lock up started after installing the new software or hardware then uninstall the same and see if the problem is solved.
2. Run the anti-virus program- In the case of sudden lock ups, you must check the anti-virus program and the manufacturer’s website for latest updates and virus definition files, because the old ones are outdated.
3. Run some good spyware removal tools- If your machine isn’t affected by any virus then download and run good spyware removal tool, such as ADWARE or MICROSFT ANTI-SPYWARE.
4. Check for free hard drive space- If there are no viruses, check the hard drive space on drive C, and ensure it is more than twenty percent or else low space leads to lock ups.
5. Check for over heating- This is caused by fans inside the case, dust builds or other problems on cooling. Ensure the power supply from fan to CPU is running and dust free. Never open the power supply cases as it contains high voltage power.
6. Check the hard-disk: Check to see if the problem is logical or physical.
7. Check the computer memory- Lock ups can also be due to the memory which fails.
8. Check for other hardware issues and update windows and drives.