Run command disappears in Start menu in windows XP

Open Windows Explorer and navigate to the "C:WindowsSystem32" directory.
Within this directory,
locate the "gpedit.msc" file and double-click on it.
 This should open up the Group Policy Editor.
 Navigate to "User Configuration -> Administrative Templates ->
Start Menu and Taskbar".
On the right side of the screen, locate the policy labeled
"Remove Run menu from Start Menu" and
double-click on it.  Set this policy to "disabled".
Click the Apply button, followed by the OK button.
Within a few minutes the Run option should become
available again.

This set of instructions will work on Windows XP Professional Edition,
but I am pretty
sure that the gpedit.msc file is not available on
Windows XP Home Edition.
 If this is the edition you are on, then go to
"http://www.kellys-korner-xp.com/xp_tweaks.htm" and
locate the link labeled "Restore the Run Command".
This should provide you with a file
that you can run and merge to your registry.
I trust this web site, but you might want to take a
look around it before you download and run this file.
Merging anything to your registry is a risk,
so it is always a good idea to make sure that you
 personally trust the source.

Something that you need to do after (maybe even before)
you restore the run command is to
 run a complete system scan with an anti-virus program
and a spyware program.
The reason I suggest this is because the only times
I have known the Run command to
suddenly become disabled is when some form of malicious
code had purposefully disabled it.
 Typically, other things are disabled, too,
such as Task Manager or regedit.

Let me know if you need anything else.