If you cannot start the computer in normal mode, you can boot up in Safe Mode and use System Restore to restore to a time when you could start the computer without errors.  To perform the System Restore, you must be logged on to Windows as an administrator.

To use System Restore, follow these steps:

● In Windows XP:

1. Log on to Windows in Safe Mode.

2. Follow the path from the Windows start menu: Start → All Programs → System Tools → System Restore.

3. On the Welcome to System Restore page, click to select the Restore my computer to an earlier time option, and then click Next.

4. Follow the wizard steps and you should be able to boot up the system in normal mode.

● In Windows Vista and Windows 7:

1. Log on to Windows in Safe Mode.

2. Follow the path from the Windows start menu: All Programs → Accessories → System Tools → System Restore.

3. Follow the wizard steps and you should be able to boot up the system in normal mode.

● In Windows 8 and 10:

1. Log on to Windows in Safe Mode.

2. From the Windows Start screen, locate Control Panel (for example, you can start typing "Control Panel" directly in the Start screen) and then click its icon.

3. Select Recovery and then Open System Restore.

4. Follow the wizard steps and you should be able to boot up the system in normal mode.