I have recently remove the lcd cable. the beeps start from bios and when start up the sound still from speakers. when i boot to windows the beeps will disable. how can i disable it in ubuntu?
What you're hearing is the system firmware on the Dell alerting you that there is something wrong with the system - in this case an LCD cable or other connection is missing and that indicates a problem in the system firmware level.
These are called Power On Self Test "Beep Codes" - they are handled at the system BIOS / firmware level, not Ubuntu, and you aren't going to be able to 'disable' those tests or the beeps from within Ubuntu. You might be able to at the BIOS level but I'd be hesitant to guarantee that.