my wmi file is missing. i am running windows xp home addition with sp3

It sounds like either the Windows Management Instrumentation Service is not running and/or your Windows Management Instrumentation information files are missing or corrupted. It is easy to rebuild the WMI information files and replace any corrupted or suspicious files.

To resolve your issue, stop the Windows Management Instrumentation service, rename the suspicious or afflicted WMI folder, the restart your system.  When the system restarts, the WMI service will start automatically and rebuild the WMI folderand it's contents automatically.

Click Start, Run and in the box enter:

services.msc

Click OK to launch the Services applet.

Locate the Windows Management Instrumentation Service.  If the Status column says the WMI Service is Started (running), right click the WMI Service and choose to stop The WMI Service.  

Respond in the affirmative if asked to stop the Security Center and Windows Firewall Services (with those services stopped your system is vulnerable to attack from the Internet so do not get on the Internet again until you restart your system).

Now would be a good time to also check the Properties of the WMI Service to be sure the Startup type is set to Automatic so the WMI Service will start automatically the next time the system is rebooted.

Using Explorer, navigate to the following folder (assuming your boot drive is C):

C:\Windows\System32\Wbem\
   
Locate and then rename the "Repository" folder to something you can remember, such as:

Repository.old

Restart the computer and then check to be sure that the WMI service has restarted automatically and that a new Repository folder has been created to replace the one that was renamed.  It may take some time to completely rebuild the Repository folder (several seconds or minutes) so wait for it to complete.
   
After rebooting, you will notice the wmiprvse.exe Service running in Task Manager and it will keep running until it finishes rebuilding the Repository.  This could take several minutes depending on your system but eventually the wmiprvse.exe Service will complete and disappear from Task Manager.

If you then look in the Event Viewer Application log, there may be some error messages like this:

Event Type:    Error
Event Source:    WinMgmt
Event Category:    None
Event ID:    4
Description:
Failed to load MOF C:\WINDOWS\MICROSOFT.NET\FRAMEWORK\V4.0.30319\MOF\SERVICEMODEL.MOF while recovering repository file.

This is normal because when the system restarts, the wmiprvse.exe process must rebuild those parts of the repository as well. It is a sequencing error as indicated below. You should not see these errors again after the system has been rebooted and catches up with itself and finishes rebuilding the WMI Repository.

Explanations for the errors seen in the Event Viewer Application log while the WMI repository is rebuilt:

Explanation
Windows Management Instrumentation might have tried to compile (mofcomp) a .mof file marked for autorecover, but the compilation failed.
This failure is probably caused by a sequencing issue.
    
User Action
To correct the problem, try to compile the .mof file again. If this does not correct the problem, contact the support provider for the program
in question.

You should not have to do anything about these error messages and should not see them again after XP has finished rebuilding the WMI Repository.

Here is some additional reading and other method to the same end:

http://windowsxp.mvps.org/repairwmi.htm