When I try starting up the SDK I get an error that says I need cache repair. I looked it up and I got an answer of opening HL2 deathmath or CS:S. It didn't help. I tried restarting steam, restarting my computer. I reinstalled the SDK, but I still get an error that says
"MountFilesystem( 221) failed: SteamMountFilesystem(948,221,0x11defc7c=,0x11defd7 c) failed with error 116: Cache needs repair."

Have you run DOD:S as well?

Yeah

http://www.steampowered.com/index.php?area=news&archive=yes&id=351
click the hl2 link and it should work, a fellow clan mate had the same problem and it fixed his.

The recent engine update potentially broke mod development tools in Steam. If your mod is based on a game other than Half-Life 2, this update causes your mod to run on the new engine. Running the SDK Launcher causes binaries to be copied from the old version of the engine cache.

http://developer.valvesoftware.com/wiki/SDK_workaround

Thank you, back up and running.

Maybe I spoke too soon... Now the props in my maps get distorted and look like some crappy modern art for some reason.
http://img127.imageshack.us/img127/4985/jerk4wl.jpg

this seems to be affecting a lot of people. Bummer. You might just have to wait until they come up with a fix.

An update seemed to have screwed some things up. Somebody suggested passing -dxlevel 80 to the Hammer application.

So, create a shortcut to the hammer.exe, located in the sourcesdk\bin directory and add -dxlevel 80 on the end of the target