Windows System Repair Tools

Startup Repair
When the Windows operating system is corrupted, whether from software vulnerability, user error or computer viruses, it may fail to boot on startup. In this case, run the Startup Repair tool from the system repair disc. This system repair tool will attempt to fix errors preventing the operating system from running.
System Restore
Windows-based computers create system restore points at regular intervals on a daily basis. If you notice a problem with your computer that you can't fix using antivirus software, use System Restore instead. Choose a date from before you were having the computer trouble, and the system repair tool will revert the computer back to that time period. Although this might fix the problem, you will lose any data or program installations from after the date you chose.
System Image Recovery
Included with Windows 7 computers, System Image Recovery lets you restore your computer if you're having problems, much like System Restore. Create a system image using this software before you ever start seeing problems. If your computer starts to work improperly, load the image you created earlier to recover your computer settings.
Windows Complete PC Restore
Native to computers with Windows Vista Professional edition, Windows Complete PC Restore allows you to create a Windows backup file. When you encounter problems, use Windows Complete PC Restore to recover the backup.
Windows Memory Diagnostic Tool
Some errors with memory can cause computer slow-downs. Rather than restore your computer to a previous state, fix the memory error with the Windows Memory Diagnostic tool. The software will check through the memory on your computer and automatically fix anything wrong. This is often the best first step if you start to notice problems.
Command Prompt
For advanced users, use command-line code in the command prompt system repair tool. If you are familiar with the command-line interface and know what needs to be repaired, bypass the previous wizard-based tools and handle the repair job yourself. This is only recommended for advanced users because you can further damage your computer if you don't know what you're doing.