Acer notebook gives continous startup beep

At a guess, given that it goes on to start properly, I suggest it might be tripping over because it can't find one of the bootable options and then it realises it cried foul too soon. Go into the BIOS settings and check the Boot Options or Boot Sequence - whatever it's called. If one of the items listed has failed, take it out of the list or take one at a time out of the list to see which doesn't cause the beep.