Serious problems with your hard drive. It may be soft errors in which case dskchk should sort it or there may be hard errors indicating physical damage which you may be able to bypass but I would not recommend it. First and foremost get any important data backed up onto an external drive. Also, if you have not yet already done so ensure that you have some recovery disks burned to recover your operating system. If you have serious problem on the drive it may be already too late to completely back up your data or create recovery disks. Then run another full disk check. If there are still errors then, provided that you have the means to reinstall your system (a set of recovery disks or a Microsoft Windows installation disk along with serial number for your pc) you should consider reformatting the drive and errors still remain then replace it.