I think your operating system is crashed or corrupted. try to boot in safe mode. for boot in safe mode press f8 at the time of startup and select safe mode. if your system boots in safe mode. If its a crash of operating system then run chkdsk for c drive and select two options with tick marks. it asks to scan at next time startup. select yes and restart your system. after scan it will fixed.
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I think your operating system is crashed or corrupted. try to boot in safe mode. for boot in safe mode press f8 at the time of startup and select safe mode. if your system boots in safe mode. If its a crash of operating system then run chkdsk for c drive and select two options with tick marks. it asks to scan at next time startup. select yes and restart your system. after scan it will fixed.