Heres my suggestion.
Go into your steam folder...
local disk > program files > steam > steamapps > common
Check for any Day of Defeat Source folder. Delete that.
then go into local disk > program files > steam > steamapps > youraccname
Check for any Day of Defeat Source folder. Delete that.
Bascially, track down and delete any DOD:S files.
If you use Steam to uninstall, it does not do a complete delete of the game files. Do a manual delete.
Then, go into Steam settings, into the Downloads + Cloud tab.
Go into download region area, and change the location to another nearby but less busy download server. Sometimes the downloads will be missing files and such.
Reinstall.
After you reinstall DOD:S. Don't run it. First, go into library and verify game cache before doing so.
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If all else fails... back up any custom content for any game you want to keep. Then entirely delete steam and go with a fresh reinstall.