It seems your partition is faulty, you can try to repair it.
If you have Windows XP:
1. Boot with the XP CD and at the setup screen press R to load the Recovery Console.
2. Choose the installation number which is usually 1 and enter the Administrator password.
2a. If you haven’t checked the drive already for errors, type chkdsk /r.
3. At the Command Prompt type FixMBR to repair the Master Boot Record on the hard drive.
4. Type FixBOOT to repair the Boot sector and make sure the boot files required to start the system are present.
5. Type Exit to quit the Recovery Console and reboot.
if you have Windows Vista and upward to Windows 10:
1. Boot with the Windows Vista or Windows 7 installation disc.
2. Click Repair your computer.
3. Click the operating system that you want to repair, and then click Next.
4. In the System Recovery Options window, click Command Prompt.
4a. If you haven’t checked the drive already for errors, type chkdsk /r.
5. Type Bootrec /fixmbr to repair the Master Boot Record .
6. Type Bootrec /fixboot to repair the Boot sector.
7. Type Exit and then click restart.
Last option to try, backup all your files and install a new HDD, your HDD might then be corrupt, run the built in dell diagnostic tools and run all the tests to see if everything is still working fine.
Hope this helps, let me know.
Ewald