iPhone won't sync with my iTunes account
Run iTunes on your computer
Drag and drop your mp3s to the open iTunes window - this will add the songs to your iTunes library
Connect the iPhone to your PC 
Click on the iPhone button once it appears in iTunes
Go to the Music tab once you entered into your iPhone in iTunes
Check the "Sync music" and "Entire music library" options as described in the first section here: http://support.apple.com/kb/HT1351
Click on the "Sync" button - this will transfer all the songs from your iTunes library to your iPhone