car does not starts sometimes.....but runs perfectly and no other issues....

The information provided is not sufficient to understand your problem. Can you provide us more details?

Are you able to crank?
Are all dash lights showing with ignition turned on?
Is the Malfunction Indicator light showing?
Do you have factory or aftermarket security system?

thanks for quick response.
engine does not respond when i try to start it. i mean it does not crank. and malfunction light comes on when ever i try to stat.
all dash lights works perfectly normal.

i think it has got smart lock security system from factory....and that's the root of all issues...

We don't have any information on your vehicle so I do not know the system used and symptoms do indicate a security issue.

You would need to have it tested and it could be a control unit fault which requires diagnostic equipments to verify. This is not a DIY job so you need professionals wth the correct tools to help you.