I have recently built my first computer and it works fine other than every so often the sound stops working correctly (it plays out only one side of my headset) I run windows vista, if i need to post more info on it i will not sure whats needed...

You may try the following suggestions/options to solve your problem:
1. Have you ever tried a different speaker for your computer? This is to see if your old speaker wire is defective or the connector from your speaker to sound card is grounded. Also check your speaker/ headphone if it is properly working too. If this is not the solution.
2. Check for the soundcard / driver is working properly. From My Computer > right click > Manage > Device Manager > Sound. Troubleshoot the sound card if it is not working properly. Try to download updates from the Internet and install. Note: check for the proper / correct soundcard driver to avoid future problems.
3. You may also remove the soundcard from the motherboard, clean the underside of the card and reseat it properly.
4. Make sure that the system is turned off before attempting the third suggestion.
5. You may also try to plug the speaker connector into the motherboard’s built in sound just to test out if the external soundcard is faulty. Remove the external soundcard and plug the speaker on the other. Test the audio if it is working correctly. Also test a different speaker / headphone into the onboard sound.