Any possible ways I can fix/ turn on my desktop?

[*C@Mi!!E*]

I've had a dell desktop for about 5 years, I've had past problems with it resulting in a new hard drive (around 2 years ago) but recently, like out of no where, something has gone wrong. Every time I turn it on a black screen pops up stating: "We're sorry for the inconvenience but Windows did not start successfully, etc." So I press the "Start Windows Normally" option, and it takes me to the Microsoft Windows xp screen, then the dell start logo, and then back to the first page I started with. I have Absolutely everything on this computer and I'm praying I could get all my files back, but I'm completely open to the fact that after a good 5 years it might be broken forever! PLEASE HELP!