Festplatte gestorben - Probleme mit Steam.

Windows neuinstallieren ist die letzte möglichkeit die mir einfällt.

Versuche das mal:

-2.Navigate to your Steam directory. (Typically C:\Program Files\Steam or C:\Program Files\Valve\Steam ◾If you wish to save your game files for a future installation of Steam, copy your steamapps folder outside of your Steam directory.

3.Delete all of the contents of your Steam directory.
4.Go to Start > Run and type in regedit.
5.For 32-bit operating systems:
In the left-hand column of your registry editor, navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Valve\.

Right-click on Valve and select Delete.

For 64-bit operating systems:
In the left-hand column of your registry editor, navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Valve\.

Right-click on Valve and select Delete.
6.In the left-hand column of your registry editor, navigate to: HKEY_CURRENT_USER\Software\Valve\Steam.
7.Right-click on Valve select Delete.
8.Close your Registry Editor.

und starte Steam mal als Administrator und versuche es dann mal zu installieren.