You need to contact the seller as it must have come with some form of warranty. It sounds like either the hard drive is faulty or your windows installation has become corrupted.
Has it ever worked, what happened since last time it worked and then not working, was there a windows update, what version of windows.
There are so many questions to be asked, we need you to give us the full info or we can't really help.
Answers & Comments
You need to contact the seller as it must have come with some form of warranty. It sounds like either the hard drive is faulty or your windows installation has become corrupted.
Has it ever worked, what happened since last time it worked and then not working, was there a windows update, what version of windows.
There are so many questions to be asked, we need you to give us the full info or we can't really help.