I downloaded Garry's Mod 8 V3b and made sure that HL2 and HL2DM were installed and run.
When I run Gmod, the Start Singleplayer Game button doesn't do anything (the console reports that the command 'showspmenu' is invalid), and no servers are to be found in the Find Servers dialog! Also, all the Gmod commands in the Keyboard Options dialog are unbound.
When I put '+map gm_construct' (sans quotes) in Gmod's launch options, it will start the map on launch, but none of the Gmod content is there. It's just HL2 with the map gm_construct being played. When I use keys to open the context menu or the other menus, the console says the various commands are invalid.
If anybody has experienced this problem and knows how to resolve it then I'd like the help... I didn't download Gmod 9 because it requires CSS which I don't have, and I don't want to buy Gmod 10.