Some older games don’t play nice with multiple CPU cores on modern computers.
However, this may not always solve the problem – if the problem has already started occurring, the gameplay may be glitchy until you relaunch the game.
One trick you can use is setting Steam.exe’s CPU affinity instead – when you launch the game through Steam, it will inherit Steam’s CPU affinity and launch with the correct CPU affinity.
Browse to the HKEY_CURRENT_USER\Software\Microsoft\Windows NT\Current Version\App Compat Flags\Layers key in the registry editor and delete any values associated with Steam.
Steam should now launch without any compatibility mode errors.
From the Settings window, click the Downloads Cloud tab and select a different server from the Download region box.
You’ll have to restart Steam after changing this setting.
If the games do not appear in your account immediately, please exit and restart Steam to confirm whether or not the registration was successfully completed.
If the games do not appear in the section once you have logged back in to your account, please submit a support request.
Steam will examine the game’s files and – if any problems are detected – will re-download the corrupted files from Steam’s servers.