|Did anything happen to it or did you make any changes to it between the last time it worked OK and the first time it didn't?|
What do you mean by 'startup page'? Is it the Dell logo or the windows logo?
What do you mean by it won't let you enter safe mode? Can you get to the boot menu screen and scroll to the safe mode option but it doesn't boot to safe mode or do you not even get to the boot menu screen?