Computers & IT Job - Worcester, WC, 6849

I have a pc that shows a black after I log in and I dont know to fix it I thinked of getting new windows,but I need the pc because all my work and school docs are on there so I need it I hope you guys can help me out. This is really a problem because I work on a daily on my pc and it will be hard if I wont have it now I really need it fixed by next week and friday for a upcoming update at my work so I hope you guys understand and can help me out.