Continuous beep sound when start up

Hello,

When i start up or reboot my dell 1564 laptop getting continuous beep sound. If i press any key then shows a blank screen with blinking cursor and beep sound, again i pressed any key then it starts normally.

After getting this problem, i had load defaults bios setup and also run the diagnostic but i don't get any error code.

what will do next..?

kindly help me..

Regards,

Nikhildas

INDIA