I suspect your "monkey.lha" is a zero-length file. You will still get a "successful" message if you try to extract from an empty archive, you just won't get any files.
Try this:
lha v monkey.lha
You should get a listing of all the files in this archive. If you don't then there is something wrong with the monkey.lha file
It should list the files when extracting as well. The OP doesn't know how to ask for help or we'd have seen the output by now.
