My macpro recently decided to stop working. I have tried to do many things suggested but nothing seems to be working. The computer turns on but doesn't not allow me to use the keyboard. So i cannot boot from a cd reset anything and so on. When it turns on i get a write screen for a while and then sometimes after a long wait i'll get the message that it cant find the os ( the folder with the question mark). So times this doesn't come up though. Any suggestions or ideas of what the problem is? Thanks a lot.