Although titled Windows – general, these FAQ’s will probably be more closely connected to XP as this is more likely to be the operating system you use.  However, in many instances, the answers given are equally applicable to other versions of Windows.

You don't password a specific file or folder, you password the profile.  This is the settings that the computers keeps about you and sets up each time you log one with your name and password

In order to introduce this security, the files have to stored on the hard disk with a system called NTFS.  Open My Computer, right click the hard disk and choose properties.  Under File System it will either say NTFS or FAT32.  Although your data should be safe, it is advisable to have a backup.

To convert a volume to NTFS from the command prompt

1. Open the Command Prompt window.
2. In the command prompt window, type

convert drive_letter: /fs:ntfs

For example, typing convert D: /fs:ntfs would format drive D: with the ntfs format.

Now you are in a position to start implement security.  To trouble shoot this look at:
You Cannot Select the "Make This Folder Private" Option for XP home, and
Disable Simplified Sharing and Password-Protect a Shared Folder in Windows XP for XP Pro

You can now right click any file or folder (from Windows explorer) and choose sharing permissions (if you want to apply this to all folders, make sure you are logged on as an administrator.  If you use passwords, make sure you have a record of them.

Remember, you can still have your computer stolen.

See also
The Ten Immutable Laws of Security

HOW TO: Set, View, Change, or Remove File and Folder Permissions in Windows XP

How do I recover lost or forgotten passwords?    

1. If there is a previous owner or user that may have the password, ask.
2. If the password used to work and no longer does, try another keyboard or try leaving the password blank.
3. The password is Case Sensitive. Check Caps Lock (Num lock on laptops as well) and try capitals combinations.
4. Try this link How to Log On to Windows XP If You Forget Your Password or Your Password Expires
5. Log in to any account that has Administrator access, then User Accounts in Control Panel. Select the user and change the password.
6. To get to the administrator login In Windows XP Home,  reboot and press F8 repeatedly as the machine starts, then select Safe Mode at the menu. Select Administrator and leave the password blank (unless there is a password). Then go to User Accounts in Control Panel. Select the user and change the password as above.  Note that If you are using Windows XP Pro and have encrypted data, you may permanently lose access to the encrypted data.
7. Call virtual riders who will either provide the solution or put you in contact with someone who can.
8. There is software you can buy to resolve this, but it is very expensive.

Finally, don’t let it happen.  Make a Password Recovery Disk (see Virtual Riders How To section) now and make sure all valuable data is backed up.

If your machine has been hacked you are likely to have an unprotected computer which gives someone else more control than you have. If this is the case then to all intents and purposes it is no longer your computer. Read this article from the BBC.

First try to determine if you have actually been hacked.  There are many things that may make it appear you have been hacked when in fact you have not.  If you routinely follow good housekeeping precautions your chances of being hacked are slim.  If on the other hand, you miss all or part of the housekeeping regime, your chances will be significantly higher. 

The best solution is to do a new installation, reformatting the hard disk.  This procedure will destroy ALL data so back-up all important data immediately.

If this appears a little dramatic, go through the good housekeeping briefing and follow it with the troubleshooting a slow running machine how to, on the Virtual Riders website.  Go to the Get Safe Online website.