Your laptop is trying to tell you what is wrong with it.
When a laptop or computer first powers on, it goes through an initial set of diagnostic tests to make sure vital components are preforming correctly. These tests are called POST or Power On Self Test. When a test fails, the user is notified via POST codes, Light codes, or Beep codes. For diagnosing Beep codes you need to:
Power on the laptop or restart it if it is already on.
Listen to the number of consecutive beeps when the computer begins to boot. Restarting the laptop may be necessary and should not harm the laptop at this time.
For common fixes read.
http://www.ithemesforests.com/dell-inspiron-fix-beeping-on-start/