Badly needed help

Hello,
whenever i start my laptop which is of lenovo it has vista in it home premium.so the problem is wen i start it shows welcome and then only a black screen appears along with the mouse cursor and a message appears that windows has stoopped working .... and it remains blank along with just the cursor for the rest of the time i cannot even format it as i have a lot of data in it .so do u know the settings by which i cannot format the d drive and only the c drive