I don't understand why under system tools "activate windows"isn't there.  We haven't been able to update anything on TWO of our computers DUE to saying not validated windows need to activate now.  When trying to activate over the internet we can't find "activate windows."  Each computer has its own COPY of windows xp.  Two work FINE and under system tools "activate windows" is there but not on the other two.  Can any one help here.  We have had these computers with windows xp PRO for a few years now.  Why lately are we having problems?Have the 2 systems had any hardware replaced  recently?or anything added?

You can reset the activate option, but it means a registry edit.

Satrt> run> regedt32.
Click file then export - this will export your regsitry in case you make a mistake and allow you to copy it back later.

Then got to HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\WPAEvents
then
'Right' click OOBETimer and select modify - change at least one of the number/letter data bits.

This disables the present product key

Now close the registry
Click start> run and type in:
C:\windows\system32\oobe\msoobe.exe /a and press OK

this will start the Windows Activation Screen.OH thank-you I will get back to you when I can,No I didn't go your way I reinstalled xp and was able to activate it right then and it was sone less than a minute and Activate windows is in system tools.  so I really don't  know what happened all this time but I will do the same to the other computer and will be fine, I hope.  thanks any way