No audio device detected

Hello,

I am having problems with my sound. It was working when I left for the day on Friday and shut down the computer and then Monday when I booted
it up, it had no sound. I went through the windows troubleshooting guide and many forum posts and here is where I am:

I have a Windows XP professional SP3

When I went into the sound and audio devices in the control panel under the volume tab it says 'no audio device'. The volume and Audio tab
are grayed out. So I went into the computer management/device manager/sound, video and game controller and found two subcategories labeled
Media Control Devices one of which has a yellow ! in front. I uninstalled the one with the !. I tried to uninstall and reinstall the
working media control device but there is no option for that. There are 3 tabs: general which says this device is working properly,
properties which has one item named mciqtz32.dll, and details which has a drop down list with device instance ID highlighted and a
description of ROOT\MEDIA\MS_MMMCI
All other components work fine. Rebooted and still no sound.

Went to control Panel/Administrative Tools/Component Services/services (local) then down to the "windows audio" service and it was set
to automatic. I restarted it anyway just to see and still no sound.

Found someone who suggested to do a system restore for a previous day when everything was working so I tried 4 different days and
every time it re-booted it said could not complete the system restore.

Thought it might be a driver problem but there is no option on the media control device to uninstall or roll back any devices like
there was on the one with the !.
I read everywhere not to do the windows update so I downloaded the Everest program and under the motherboard tab it said

CPU Type AMD Sempron, 1833 MHz (11 x 167) 2600+
Motherboard Name Gigabyte GA-7VM400M-RZ (3 PCI, 1 AGP, 2 DDR DIMM, Audio, Video, LAN)
Motherboard Chipset VIA VT8378 UniChrome KM400
DMI BIOS Vendor Award Software International, Inc. DMI BIOS Version F5

I went to Giga-byte.com and downloaded the Realtek AC97 Driver. I unzipped it and did the setup and reboot but still no sound.

I got another idea from someone who had the same problem to do the following:
* Copy C:\WINDOWS\inf\machine.inf to a temporary location
* Edit your copy of machine.inf in Notepad
* Remove line 20 (ExcludeFromSelect=*)
* Right-click “Plug and Play Software Device Enumerator” and click “Update Driver”
* Choose “Install from a list or specific location (Advanced)” and click Next
* Choose “Don’t search. I will choose the driver to install” and click Next
* Click “Have Disk”
* Browse to the location of your copy of machine.inf and click OK
* Select “Plug and Play Software Device Enumerator” and click Next
* Wait for the software to install then click Finish
It completed the install successfully but no sound.

Someone elses similar advice:
1. From Device Manager (be sure to select View/Show hidden devices),find the 'ISAPNP Read Data Port' device from the System Devices list.
(Of note: once I successfully repaired this problem, this device no longer appears.) 2. Right click the ISAPNP device, and select
"Update Driver" 3. Select "Install from a list or specific location" 4. Select "Don't search. I will choose the driver to install."
5. The step I left out on prior trials: UNSELECT "Show Compatible Hardware" 6. Be sure that "(Standard System Devices)" is selected under
Manufacturer. 7. Under Model, scroll down until you see "Plug and Play Software Device Enumerator". Select this item, and select "Next>".
8. You will receive some frightening error message that you should probably disregard. 9. Complete the installation of the driver.
You will see your device list magically change before your eyes. The other PNP devices will mysteriously become enabled and active.
If not, restart.
It completed the install successfully but no sound.

Any new ideas?
Thanks for your help!

Melissa