I've downloaded SDK, SDK Source Base 2006, SDK Source Base 2007. I've ran HL2 once. Upon trying to start Hammer, I get a circle mouse icon for a few seconds, then nothing happens. I've selected SDK Source Base 2009 as default and TF2 at the bottom, yet nothing changes. All the other options work, such as Model Viewer, etc. An obvious solution would be that I haven't downloaded Source Base 2009, yet I can't find that on Steam anywhere. Any help would be appreciated. Thank you!