My only suggestiong is that you paste the error next time, instread of making us guess at what it was.
I'll take a wild guess, that nagios is telling you it can't find any hosts, services, etc. in any configs.
That's because you haven't told nagios where all your config files are located.
Here is what part of my nagios.cfg looks like. I'd strongly suggest you do the same.
# Misc commands (notification and event handler commands, etc)
# You can split other types of object definitions across several
# config files if you wish (as done here), or keep them all in a
# single config file.
# Extended host/service info definitions are now stored along with
# other object definitions: