Also if you're in win7, make sure that in the audio mixer, the sound for your browser is set to a comfortable volume.
In your systray, click the "speaker" icon, and then "Mixer".
The different applications for which you can modify the volume have each a volume channel. Make sure that the channel with the browser you're using as an icon is set to a high volume, and that the master volume is set to a good volume too.
Else, as naelian said, there might be an issue with the record volume of your samples, if so, try to normalize them in a sound editor, making sure they are louder but don't make the speakers saturate (no peaks over 0 db).