Thanks for your response. I already done as u suggested. but i'm not able to enter into bios. it is restarting with in 2 or 3 seconds at that time if i press 'del'or f10 i'm not able to enter into bios. hard disk drive is not booting. it is restarting again and again. if i press 'esc' button the power is 'on' hard disk not botingand at that time if i insert any bootable disk it is not booting.