Finding a WON CD Key in the Windows Registry

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=199

If you installed the original game off a CD but no longer have your original CD case with the CDKey printed on it, it is VERY IMPORTANT for you to go copy and save this key otherwise you will have to purchase a new copy of the game.

run START > RUN > regedit then browse to:

[HKEY_CURRENT_USER\Software\Valve\Half-Life\Settings]

and look for "Key", and copy that number down.

If you installed Counter-Strike or DOD your key might be located in that registry entry instead of "Half-Life"

Steam does not store CDKeys in the registry.

CAUTION: Valve strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Please refer to this Microsoft Article for more information about your registry.