... my laptop get's restarted after display of Windows.
From your description, I'm not clear what actually happened.
1. Do you mean that it starts to boot to Windows and then continually reboots?
If so, that could indicate a virus infection. However, you said that you re-installed Windows, and the problem continued.
2. Did you do a clean installation, either from the recovery partition or from a recovery DVD, or did you try to install it while saving your old settings?
If you tried to save your old settings, a virus could still be present in your restore points or swap file. If so, it would probably try to reassert itself on the new installation. A full, clean installation should resolve that.
If you were able to complete a clean installation, my first guess would be that it probably isn't your CPU. The easiest and least expensive thing to test would be your RAM. If you have more than one stick of RAM, try removing one and booting with the other. If the problem continues, try the other stick. If the problem still continues, try to borrow other RAM to test your machine.
It could also be your hard drive, which is the other part that's easy to test because it is intended to be field replacable. However, if you can't boot to the desktop (continual rebooting), you would have to test the drive by connecting it as a slave to another drive to test it as
bailw suggests.
If something else on the motherboard has failed, it may cost more to repair it than to replace it so do as much testing as you can without spending a lot of money.
It sounds like you may not be not very experienced at servicing your machine. If not, I would recommend getting some help from a more experienced friend or from a professional service technician.
Hope that helps. Good luck.