Enable Volume control and playing any sound file

I have a problem in my laptop. My laptop is working on the ubuntu 10.04 OS. I changed my login from 'administrator' to 'root'. Now, my login through 'administrator' is also not working. Recently, I'm not able to hear any sound while playing any sound file. I do not hear even the star-up sound. The volume control icon is showing 'mute'mode. I'm unable to set it right. I tried all the tips like System>Preferences>Startup Applications. Click +Add, then input: Name: Volume Control Command: gnome-volume-control-applet Comment: Launch volume control applet Please, help to solve these problems. Looking forward to a working reply.