Inspiron N5050

Hi, I own a Dell Inspiron N5050 i5 processor laptop with 4 GB RAM and 500 GB hard disk. It’s getting around 14 months since I bought it. From the last few days, I could see that the machine makes beep sound on start up till the windows starts. The sound gets disappeared after OS starts. Especially if I turn on the laptop from hibernation mode, sometime rebooting also make the beep sound. However, I observed a similar low tone inside the system even when the machine is running. All keys are working fine no thing is jammed. Drivers are all updated the processor fan is also running correctly. I have performed the dell H/W diagnostics test and it gives generic windows IO error. What should I do?