This is what i got told to do by steam support and i just wanted to share it to everyone else that is having the problem. Note this may reset your stats


-If you are running in Windows Vista or Windows 7, please completely exit Steam,
and right-click on the shortcut which you use to launch Steam and select "Run as
Administrator."

-If you are running in Windows XP, take the following steps:
1) Exit Steam.
2) Go to the "Start" menu, select "Run", type "regedit" and click "OK".
3) Navigate to the following registry key: HKEY_CURRENT_USER\SOFTWARE\VALVE
4) Right click and select "Permissions"
5) Check the boxes for "Admin" and "System" to "Full control" and "Read".

First, verify the GCF Cache for the game:
Title: Verifying GCF Cache Files
Link: [ Register or Signin to view external links. ]

Verifying the GCF Cache solves most CD Key issues for most users.

NOTE: The CD Key for this title is not shown to the user in Steam.


If it still does not work, please try deleting your Call of Duty 4 registry
entry:

Go to the "Start" menu, select "Run", type "regedit" and click "OK".

If you are using a 32-bit version of Windows, navigate to the following registry
key: HKEY_LOCAL_MACHINE\SOFTWARE\Activision\Call of Duty 4
Note: In 64-bit operating systems, this path may begin as: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Activision\Call
of Duty 4

The contents of the registry entry "codkey" is your CD Key. Please write this
key down for future reference.

Right-click on the entry "codkey" and select "Delete".

Exit regedit.

Restart your computer.



Log in to your Steam account using the following instructions:

-If you are running in Windows Vista or Windows 7, right-click on the shortcut
which you use to launch Steam and select "Run as Administrator."

-If you are running in Windows XP, ensure the the following steps have been
taken before starting Steam:
1) Exit Steam.
2) Go to the "Start" menu, select "Run", type "regedit" and click "OK".
3) Navigate to the following registry key: HKEY_CURRENT_USER\SOFTWARE\VALVE
4) Right click and select "Permissions"
5) Check the boxes for "Admin" and "System" to "Full control" and "Read".


From the Library list, right-click on "Call of Duty 4" and select "Properties"
from the menu.

Select the "Local files" tab and click the "Verify integrity of game cache..."
button.

Steam will verify the game cache files (GCF's) - this process may take several
minutes.

Once the process is completed, the "Check" window will automatically exit and
you should be able to launch your game.

You may also try using the key previously found in your registry if COD4 asks
for a CD Key again. I hoped it worked. Plz Thanks the topic and rep if it worked