Help Needed: "No audio output device is installed"

I have a Medion Laptop model MD96015.
When I brought my laptop it came with Windows XP, but it had a sticker saying it was Vista Compatible.

A few days ago I loaded Vista Home Premium on my computer, and I got everything working except my sound.

When I go into device manager it says that "SigmaTel High Definition Audio CODEC" is working properly, and when I click update drivers it tells me my drivers are up to date. I tried going to the medion website and downloading the audio drivers they provided for my laptops model number, but after installing them, I still don't have any sound.

On my taskbar there is the speaker symbol with a cross over it, and if I put the mouse over it it says "No audio output device is installed"

I have tried uninstalling the drivers and reinstalling them again, but it doesn't seem to work. I'm out of ideas now, so please, help!!

ok, i need you to do something for me SamanthaAmy, can you go back into the device manager, and above the devices, theres a button that looks like a spyglass over a computer. click on that and tell me if anything happens

When I click that it says "Scanning plug & play compliant hardware" & then the list refreshes and thats it, nothing else happens.