My Dell laptop could not start but keep beeping with screen black

Recently, I have faced a problem with my Dell Inspiron 5520 (Windown 8). After I press the power button, the windows cannot start and the screen keeps black. The three buttons on the top, right corner of keyboard (i.e., Dell Instant Launch button, Dell Audio with Preset Switch button, and Windows Mobility Center button) flash from left to right and then from right to left, then stop flash and my computer starts to beep and keeps beeping for long time. I have to disconnect the power cable and reconnect to try several times to start my computer. Sometimes I do start windows after trying several times. would you guys please tell me how to fix this problem? I got my laptop in the end of 2012. I do not use it too much and only less than 20 hours a week. Does anyone has the similar problem?