ITunes deleted some of my songs after I plugged my iPhone in?

When I tried to download my iPhone songs onto my new computer's iTunes account, it deleted about 240 songs and left me 27. I don't know what happened. When I logged out and tried to log back on, the 27 songs were still on my iTunes but they rest of my 240 some songs were gone.

Was the computer registered to your iTunes account? Did you hit sync all when the 240 were manually synced?