Acer aspire 4741Z

Hello,

I have acer aspire 4741z laptop for last one year, now on switching on the laptop sometimes it make a beep sound and sometimes not and it does not start, screen goes black nothing can be viewed, but if laptop is set off and switched on and F12 key is pressed a menu comes and then enter key is pressed then laptop starts and all the work can be done i.e. typing, reading, using internet. Someone says have to replace keyboard, some says to replace mousepad some says have to replace bios of motherboard. please suggest what to do?