A black screen being showed after the windows logo

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Hello,
I have a Dell VOSTRO 1450 with windows 10
From sometime there is a Black screen is coming after the windows logo and again the windows logo comes and then the sign in panel comes.
I've also tried to format the C drive and reinstall windows but no luck.
But now i cannot format my c drive i have many files in it.
Plzz help me.