Just needed some serious help here...my Laptop (OS Windows 8) just could not start due to eror on C: as it appears everytime I open it... At first it says "diagnosing your PC" afterwards it says "Scanning and Repairing Drive C: (with percentage)"...then goes back to diagnosing PC... it just repeated itself on cycle... and sometimes other things appears like "Repairing your Driver. This may take longer than an hour." and stuffs like "Repairing Windows://?-AHSDGHKDHFD5615D-561564584848-SG648D4V958F45G4-SDFBKH" something like that... I never got in to log in page... and sometimes blue screen appears saying "Your PC ran to an error. We are collecting error reports and will restart for you (with percentage)", then back to diagnosing again...

Method 1: Perform an Automatic repair.
The Automatic repair can detect and fix the issues that prevent the computer from starting normally. You will need the Windows 8 installation disc to perform an Automatic repair. If you don’t have a Windows 8 disc, I would suggest you to download the Windows 8 installation files from another computer through this link and choose to create an installation media when the upgrade assistant prompts.

After you have a Windows 8 installation disc, follow these steps:

When your computer starts, wait for the manufacturer logo to check the option for boot menu, it will usually be F12.
The boot menu key might differ with each manufacturer. If you are unable to find the boot menu key, you may refer the user manual.
Restart the computer, when the manufacturer's logo is displayed, keep pressing the Boot menu option key to enter the boot menu and change the boot option to CD\DVD ROM.
After you boot your computer using Windows DVD or System Repair Disc, a black screen appears with gray text "Press any key to boot from CD or DVD". Press any key.
Select the correct time and Keyboard type.
Click Repair your computer in the lower left corner
Click on Troubleshooting, advanced option and then click start up repair.

If you are still unable to boot you can perform the following steps.

Method 2: Perform System Restore or Refresh.
Follow the steps given in the method 1, in the step g) select Troubleshooting, advanced option and then System Restore.