Do you have the memory upgrade? Try (carefully) removing that and see if the problem still exists. If it now works all the time, put the memory back in, ensuring it is down in place firmly (don't break it!) ensuring it is seated correctly. If the problem returns, it's probably faulty memory.
first of all thanx for your time.what s the exact meaning of the upgrade memory.i had erase all the autoload song but not the autoload folder.has this any importance with my problem?thanx again p.s morebucks u are a real funny guy.peace