As both the center channel and sub share a line, I would venture to guess you have the cable plugged into the wrong jack, the jack is damaged (either on the speakers or motherboard) or the cable is damaged.
Go into your Sound settings from the control panel.
Click on your playback device (should say Speakers' with C-Media CM 6501 below) then select 'configure' at the bottom.
Here you will be able to chose and test your multi-channel output.
Make sure 5.1 Surround is selected and hit 'Test'.
If sound does not play through the center and sub, switch the Front speaker cable to the Center channel on your motherboard.
Manually press the Center and Sub icons.
Does the sound now play through the front pair?
If so, the issue is with your speakers or the wiring.
outlw6669 when you say go in to the sound setting,are you meaning the setting for the CMI CM6501 ?
And to answer the other question all speakers do work as well as the Sub.How i know this is cause I unplugged the Sub and plugged it in to where the speaker are plugged in.This is a onboard sound card.I do not have a installed sound card.Their is no and I mean no 5.1,but there is how every a 7.1 suround sound.
I do not think I will every get this to work right.I sure miss the bass ect wroking right.
If you are sure all the speakers are working fine either the system is configured for Stereo output only or the jack is damaged.
Check as with the above to ensure you are properly set to use 5.1 surround and to test all your speakers.
Also, make sure the cables are plugged into the proper jacks..