macbook is not open in macintosh after windows failure?

[Jaiff]

hello,

I don't know anything about software OS windows i bought an old macbook from someone about 4 months ago it was working fine. when i start macbook there come two options mcintosh MD and windows i select macintosh MD enter password do some work and close it. But today when i open my macbook it doesn't ask those option it automatically run window and it shows safe mode, safe mode networking and normal window i select normal option and it goes to startup repair the it failed showing some error that startup unable to repair or something and macbook goes off. then so on when i open again again it happen.
what should i do please help me

Thanks

 

[ktolo]

Sounds like either the filesystem is corrupted or the hard-disk failed or partially failed, resulting in filesystem corruption.