Hi S1ke,
To fix this problem you need to exit from Steam (if it's running) and delete a file in your Steam directory called:
ClientRegistry.blob
This would typically be in:
c:\Valve\Steam
or
c:\program files\Steam
The next time you start Steam it will re-create this file, do a brief update and then you should be able to play.
If this does not work let us know!
Thanks,
Ric.