It's first time when i use ubuntu.I downloaded and installed 12.04 version of ubuntu.It works fine but sometimes when i shut my pc down from ubuntu and i try to start it again,nothing shows on the screen.It's always black and it shoud appear Acer logo(i have acer aspire 5573)It's like the sistem is restart again and again but it can't boot ubuntu(or windows,i use dualboot)The meniu(where i can choose between windows and ubuntu it's not displayed because the pc don't start correctly.When this happens i shut down the pc definitively and i remove the battery and i put it again.Then everything works fine.How do i repair it?I think that could be a incompatibility with the pc because with windows everything works fine.Help please and sorry for my horrible english...Thanks!