I have a problem with booting up. Every time it gets to the user screen either I pick one and then a password screen flashes for about a second then it reboots and continues to do this. If I hit F8 and pick last known good boot it will start fine. Sometimes I get a password screen that says "not authorized" before looping. Any and all suggestions will be appreciated. I have ran spybot S&D, McAfee and they both say the system is clean.