Do you mean you played the song that was on your hard-drive, or you played the song off the CD using your comp?
If the song is quiet on your HD then it's a mixing thing and you need to crank the master volume and check the export settings in whatever program you used.
Speaking of which, it would be helpful if you told us what you were using.
The hard drive of the computer, since that is what you used to burn the song to disc.
You burned the song to your PC, btw.
With technical stuff it's rather important you tell us everything and use the right terminology.
Is there anyway to control the levels of the tracks going into your computer from the Yamaha? If there is, there's a possibility that you may have had the levels down when transferring the files to your computer. Also, what program are you using on your computer to burn the music onto a compact disc?