Here is the video tutorial link :
Youtube.com
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Also this is a tutorial for the steam version of the game ! I don't know if this works on the retail version or not.
And here is the text version :
Step 1. : Press "Windows key" and "R" key at the same time to get a window called "run".
Step 2. : In the "Run" window type "regedit".
Step 3. : While in "regedit" navigate to : HKEY_LOCAL_MACHINE/SOFTWARE/Wow6432Node/GSC Game Wold/STALKER-SHOC
Step 4. : Add a string called "installvers".
Step 5. : Edit the "installvers" string and change the value data from 1.0005 to 1.0001.
Step 6. : Download and install patch 1.0004 US version (Only the US patch will work but don't worry you can still play all of the mods!), you will run into an error saying something about the readme.txt file, don't mind that error ,just close the installation.
Step 7. : All of the content that is installed to "C:\Program Files (x86)\THQ\S.T.A.L.K.E.R. - Shadow of Chernobyl" copy it to YOUR stalker shoc installation folder.
Step 8. : Delete gamedata.dbc and gamedata.dbd.
Step 9. : Go to your steam library, then to launch options and imput this value : -noitro
Step 10. : enjoy your game!:D