Before answering your question, could you please tell me which OS you had before switching to Vista Ultimate?
How old is your mobo?
If it is very old, I suggest flashing your BIOS.
Or, check out your configuration panel for possible devices problems.
To do so: > go to the 'Start' menu
'click on the control panel'
> then click on the 'device manager'
o if there are any yellow question marks, (it means that your sound driver is not properly installed) you need to install your sound driver again.
o if there are any exclamation marks, (it means that there is a conflict with your sound driver), try to update your driver, or if there is no new version of it, uninstall your current driver and try to reinstall it.
Hope this helps