Error on login #584

I have hello system installed on my HD right now and it's okay, but sometimes when i turn the computer off and the utrn it on and try to login it randomly stop working and freezes at the login screen without loging me in and neither letting me click on anything or do anything the only apparent way to resolve this is by rebooting the computer but once it happens the first time it happens again every other time and i can only use the system normally by reinstalling it.