If C::B suddenly stopped working, that means if you ever have been able to start C::B and close it cleanly, the
default.conf surely exists.
Uninstalling C::B does not remove it.
As posted I don't know the location on neither on vista nor on win7, but you can try the following command from the command-prompt (Not sure if it still works on win7):
it should point you to the directory, where you find C::B's conf-folder (named
codeblocks and containing at least
default.conf).
To verify, whether your
default.conf is broken or not, you can also start C::B from the command-prompt (if it still exists on win7) with another personality :
where test is the name of the personality, you can use everything except "default" .