cgminer fails to start with error "error opening terminal: dumb"
I had the same problem and for me it worked to set the TERM variable to nothing directly before you execute cgminer. Like this in the cmd shell:

set TERM=
cgminer-nogpu.exe ........

If you set it to "" (meaning nothing) in the system settings it will use the default value "c:\windows\system32\cmd.exe". You can check the the variable in the shell with:

echo %TERM%

I hope this will help you :)