I bought a laptop from a friend and it was running really slow. So I got a windows xp cd and tried to reformat and completely clean it. When I restarted it, it now says ntldr is missing. I have no clue what to do but the windows xp cd is an upgrade cd, so I thought that would be the problem so I tried to find another os cd but all they sell are windows 7. So I got that but it starts loading then says a driver is corrupted. I don't know what else to do.