new inspiron 5558 beebing 8 times on startup

Hello,

I have a problem with my Dell  insipiron r15 5558, I bought it 3 months ago. But since a month my laptop Beep's 8 times at the start-up. when it does I usualy just power off my laptop because of the annoying sound, and turn it back on. Once I powered it on and off for 3-4 times it doesn't beep anymore an works fine. Does anyone know what the problem might be? I  ran an LCD Test as well as Pre-boot System Analysis,it ran well without any problems, i used my warrenty  and sent the labtop to dell center here the last 2 weeks they sent it back and said there is no problem with my laptop , but it still beebing 8 times on clicking the power on

PS. Sorry for my bad english

BTW. I'm was running  Windows 8.1 pro 64 bits
i upgraded it to windows 10 and went back to 8.1 and the same problem
now im running Windows 8.1 pro 64 bits