I have similar issue. Start8 displays Programs and Control Panel results for me. No file search results at all. My search service is running and all items are indexed. Files search works on the Start Metro screen properly.
Do programs and control panel fill the entire list?
If so it sounds like the OS is telling Start8 the indexer is disabled.
If you click on see more search results do you see the results you expect?
Also if you reboot does the problem continue?