Okay, so after you log in the screen turns black and you can only see your cursor? Well the solution to that is, press Ctrl+Alt+Delete. After this you should see the following (or at least some of the following): Lock Computer, Logoff, Shut Down, Change password, Task Manager, and Shut Down.
Click Task Manager! After this at the most eastern bottem of Task Manager, click New Task (I guarentee it should be there), there should be a window (short and rectangular), then type in "explorer" (NO CAPITAL AND EXACT FORMAT IN QUOTES
(NO QUOTES). Hit enter or click "ok" that should do it :)