Hi

I have new HP Pavilion 15 laptop which ships with a win 8 os. i have install centos 6.3 on with dual boot i have installed Centos 6.3 on it but i am unable to boot centos when i start system it directly goes to windows8 , not even shows grub boot loader. please suggest how have a dual boot on it.

If you have windows 8 as an OEM install, you probably have 'Secure Boot' and it needs to be disabled. You would have to check the BIOS on boot to see how to do it. Probably would be a good idea to go to the HP site and see if you can find something specific for your computer.

I have already disabled secure boot but no luck.

I've read that Win8 will only work on UEFI based systems. Was the install of grub UEFI enabled, do you know? It sounds like an entry in the efi menu has not be added or the efi/bios is not recognizing the entry. Also, some laptops have been known to be bricked (some Samsungs) by attempted UEFI installations. Some googling about your specific laptop to see if anyone has had success installing any Linux Distribution would be a good idea.

<edit> Come to think of it, I think those laptops were actually netbooks, but I hope you get my hint that perhaps you need to search for evidence of:
1) someone successfully install linux on that laptop
2) information on how they did so
</edit>