I am trying to open windows on the internet but am getting message written "the requested look up key was not found in any active activation context".What do I do?Thank you in advance!

Step 1:Uninstall Internet Explorer 7 and check if the issue is resolved: How to uninstall Internet Explorer 7 (http://support.microsoft.com/kb/927177/EN-US)
Step 2 : Repair Internet Explorer 6 by using the System File Checker in Windows XP.

If you already have Windows XP Service Pack 2 installed, and you do not want to install Internet Explorer 8, you may be able to resolve problems with Internet Explorer 6 by running the System File Checker.

To run the System File Checker, follow these steps:
1. Click Start, click Run type sfc /scannow, and then press ENTER.
2. Follow the prompts throughout the System File Checker process.
3. Restart the computer when System File Checker process is complete.

You may also refer to: How to reinstall or repair Internet Explorer in Windows 7, Windows Vista, and Windows XP (http://support.microsoft.com/kb/318378)

Source: Microsoft Answers (http://answers.microsoft.com/en-us/ie/forum/ie8-windows_other/the-requested-lookup-key-was-not-found-in-any/5fd9fcf1-cac4-411e-a66a-8f19d8b73586?tab=AllReplies#tabs)