Laptop beeps on startup

I have a Dell Inspiron 3421 laptop with windows 10 64-bit OS. Recently i am facing a problem on it. When i pressed power button, it shows up dell logo and then it starts beeping until windows logo become appears. After windows logo appearing it stops beeping. In the time of beeping, if i press any keyboard button it stops. But i used a keyboard tester and none of the key found to be automatically pressed ( all keys are working fine). What can i do?