If the computer just hangs while loading operating system, then restart it by pressing the Reset button. After I start booting from the hard disk, press F8. Wait for the opening menu containing alternative options to continue to download.

Click "Run last known good configuration". Wait for a while. If the computer hangs again, repeat the login procedures described in the menu. Select "Windows Safe mode". After some time the system will boot in the selected mode. Open control panel and navigate to "Backup and restore".

Go to "Restore system settings". Click the "Launch system restore". Select a control point from the list. Specify the system files that was created before the problem occurs. Click "Next" and confirm to start the restore of the operating system. After the reboot, select normal mode operation of the OS.

If the system does not boot even in safe mode, then use the recovery disc. Insert the DVD in the DVD drive and restart the computer. If you have disabled booting from the disc, then hold the F8 key. In the opened menu select the required DVD drive.

When working with Windows 7 or Vista, follow the step by step program menu drive until you see the "advanced recovery options". After navigating to this menu, select "startup repair". Confirm a carry out the necessary operations. Wait until the computer is restarted. Restore a system after gaining access to the functions you need.

If you are using Windows XP, then press R after opening the corresponding menu. Run the recovery program boot the operating system.