I just replaced the power

When you play an audio file it does not tell you that it is not able to play because there is no sound device?

Ok then what you will need to do is Go to Control Panel Doubke click on Sounds and Audio Devices...Ensure there is no check mark in the Mute section
Go to the Audio tab and ensure that you have a Default Playback device if you do not try to select the one you installed from the drop down menu.

If this does not work then you will need to right click on My Computer click on Properties then select the Hardware tab then click on the Device Manager Button. From there you will need to look for the catagory called Sound Video and Game Controller to see if you sound card has been install properly if it has not been instsalled properly then you will see a ! or a ? where the device is. If you are able to provide the type of audio device I can find you the driver.