Sounds like you're trying to download a fake file. Is it a new release, or really popular file, with heaps of sources? Does it sit connecting for ages & then go to 'need more sources'? Search again. Vary your search terms, look for artist or album rather than song title. Try the All Types search. Stay away from files with heaps of sources, go for a file with 10 sources or less.
These fakes are common now & are a pain

Running as an ultrapeer shouldn't effect your ability to download. The network will choose you to be an ultrapeer if you meet the criteria & ultrapeers are needed. To become an ultrapeer, what's needed is a reasonably fast connection, high uptime & no firewall blocking. So, no... not everyone would be able to become an ultrapeer.