Hey again,
In that case it might just be simpler to do:
sed -e 1,2d -e 6d FILENAME
The reason the command above removes any line starting with a pound is that I write answers in too many different languages

The proper syntax for this command (although, actually, it was syntactically correct (no errors) but didn't do what was expected) would be to do:
sed '/^#\(ifndef\|define\|endif\)/d' FILENAME
Best wishes,
Mike