Almost all of Windows' built-in services use SVCHOST.EXE. Turning off Aero might work, but only if the DLL responsible is corrupted. In short, you're almost screwed. You've got a couple of options:

1. See if you can verify the digital signatures on all of the supposedly-signed DLLs in the Windows directory and below. I think that SysInternals have a tool that does this. This'll tell you what needs replacing.
2. Break out WinDbg and get medieval on it.
3. See if a Windows repair will fix it.
4. Nuke the site from orbit.