i have a macbook pro and when i turn it on just appers white screen whith a folder sign of interrogation... i'm sorry for my english......what could do to fix this

Do you mean a folder with a question mark on it? If so it means the machine can't find a valid start-up drive. Which means either the system is corrupt or worse case scenario the hard drive has failed. Try booting from the install DVD and run Disk Utility to repair the drive.