Here is the page where you can download the owners manual pdf click here
Dell diagnostics page 48 says to press F11 at the Dell Logo on Boot Up. This brings up a menu to choose from, including Safe Mode.
If you can't get it to boot to safe mode the pc may have Spyware/virus that has caused the logs off as soon as logged in problem.
This microsoft KB explains more click here (though I doubt you will be able to use the suggested solution as need to be networked and do it through remote access)