After a Compiz crash, Steam refuses to start.

[MowdownJoe]

I had Compiz crash recently, and had to hard-restart my machine. (I couldn't even get to a terminal!) Upon restarting, Steam tried to download an update. It never launched after trying to unpack the runtime. I tried launching Steam again, and it tried to unpack the runtime again and gave an error about Steam already being running. (System Monitor didn't see any Steam-related processes running.)

When I run Steam from the command line, I get this:

Running Steam on ubuntu 13.04 64-bit
STEAM_RUNTIME is enabled automatically
[2013-06-30 11:01:56] Startup - updater built Jun 28 2013 15:12:19
[2013-06-30 11:01:56] Opted in to client beta 'publicbeta' via beta file
Installing breakpad exception handler for appid(steam)/version(1372460154_client)
Installing breakpad exception handler for appid(steam)/version(1372460154_client)
[2013-06-30 11:01:56] Verifying installation...
[2013-06-30 11:01:56] Verification complete
unlinked 0 orphaned pipes
Gtk-Message: Failed to load module "overlay-scrollbar"
Installing breakpad exception handler for appid(steam)/version(1372460154_client)
[0630/110157:WARNING:proxy_service.cc(958)] PAC support disabled because there is no system implementation
/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/steamUI/../common/steam/client_api.cpp (287) : Assertion Failed: ClientAPI_InitGlobalInstance: InternalAPI_Init_Internal failed.

Assert( Assertion Failed: ClientAPI_InitGlobalInstance: InternalAPI_Init_Internal failed.
 ):/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/steamUI/../common/steam/client_api.cpp:287

Installing breakpad exception handler for appid(steam)/version(1372460154_client)
/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/steamUI/SteamStartup.cpp (648) : Assertion Failed: ! "There was a problem with your Steam installation.\n" "Please reinstall steam.\n"
Uploading dump (out-of-process) [proxy '']
/tmp/dumps/assert_20130630110157_5.dmp
Shutting down. . .
unlinked 2 orphaned pipes
[2013-06-30 11:01:58] Shutdown
CAsyncIOManager: 0 threads terminating.  0 reads, 0 writes, 0 deferrals.
CAsyncIOManager: 88 single object sleeps, 0 multi object sleeps
CAsyncIOManager: 0 single object alertable sleeps, 1 multi object alertable sleeps

Now, I see the two "Assertion Failed" lines. I've already tried uninstalling (specifically, with

sudo apt-get purge steam-launcher

) and reinstalling. That did nothing. I also tried deleting clientregistry.blob, and that also did nothing. Any help?

[Dusk of Oolacile]

You could try backing up your game data, then erasing the whole steam directory (in ~/.local). The bootstrapper should download all files for you. Then move your game data back to where it belongs.