Don't panic, its general problem. Our Global Laptop Care Engineers gives two solutions, you can apply them by your own without going to any repairing center.
Generally, Due to dust on fan inside the laptop or CPU the computer restarting problem occur. So, you have to take off the computer cover, clean out the inside well you can, check fans. Turn on the computer you will find that your computer restarting problem has been solved without paying any cost for this.
Sometimes dust inside laptop is not responsible for restarting the system. Our Global Laptop Care Engineers suggest you the next one more solution. You have to Click on Start-Programs-Start Up. If there are any listings in the Start Up area, you need to delete as many as you can.(Right click the listing and choose 'Delete') Please remember that these are just shortcuts to programs and not actual program files, so its safe to delete them. Don't get rid of some that you really like like Microsoft Shortcut Bar or any others that you really want on the screen when it starts. Then click on Start-Run, in the typing area put 'msconfig' (without the quotes), press Ok. When the System Configuration Utiltiy box opens, click on the Start Up tab. You will see a number of listings with boxes and check marks in them. These are programs that run at start up. You can safely uncheck many of the boxes. Don't uncheck System Tray, Scan Registry, or your Virus Scan startup programs. After you’re done, click 'Apply', then 0K, and the computer will ask you to restart. Do it and then check your resources again. Hopefully they are much higher (Don't worry too much, if you make a mistake you can always go back to this box and put a check back in any of the listings you want).