"What would be the reason and what shall I do? "
It gets too hot. Clean it.
Files have been corrupted. Run CHKDSK.
Old/bad drivers. Update.
Malware. Remove it.
Failing HDD. Replace.
Failing battery. Replace.
Failing charger. Replace.
With more information, we could make a better diagnosis.
Part 1: Asking a question 0. Nothing Illegal We aren't going to help you find a CD key or Serial Number, and we aren't going to discuss software you've downloaded or movies you are trying to get or obtained illegally. Take those questions elsewhere. Don't complain when your thread gets...
Most problems can be better identified than 'it crashes'. ComputerHope website might help you be more precise.