When I try to run chocolatey from the Command Prompt, it gives me this error:
The system cannot find the file C:\Chocolatey\bin\chocolatey.exe.
I've tried changing the environmental variable, but then it gives me (almost) the same thing:
The system cannot find the file C:\ProgramData\Chocolatey\bin\chocolatey.exe
You'll need to provide more information here. This is not enough information to make a reasonable determination of your situation.
UPDATE: Try reinstalling. If that doesn't work, try a where.exe choco
to try to determine where it is looking for the executable and if there is any conflicts. The last thing one could do is back up the lib/bin folders (minus choco.exe executables in the bin directory) and blowing the rest away and reinstalling. Plus maybe a restart.