Windows 7 Sound gone after Sleep mode Help

Go to Step #3 Update Drivers, read the first paragraph.

Then scroll down to Windows 7 and follow the instructions for updating.

But, before you check for updates make sure you go to: Control Panel\All Control Panel Items\Windows Update\Change settings and have all the boxes checked, You may also want to change the way it updates by Opening the Important Updates box and choosing "Check for updates, but let me choose" option, click OK, then run updates.

This will check to see if there are any updates for your sound equipment.

Let me know if, when you type update in the search box if you see any other options for updating like for your gigabyte MB or Device Drivers, okay?

I have to go out for 'bout an hour, but I'll will check back.

Then go ahead and start the update for the SP1, that alone may correct the problem your having.

Before you begin

Before you install SP1, we recommend you do the following:

• If you have any prerelease versions of SP1 installed, uninstall them before installing the final release version of SP1. To do this, follow the instructions in "Uninstalling SP1" in this topic.
• Back up your important files to an external location, such as an external hard disk, DVD or CD, USB flash drive, or network folder. For more information, search "Backing up files and folders" in Help and Support.
• If you're using a laptop computer, connect it to an AC electrical outlet and don't unplug or restart the computer during installation.
• Some antivirus software might prevent SP1 from installing, or might slow down the installation. You can try temporarily disabling your antivirus software. If you do so, be sure that you're aware of the risks involved, and be sure to re-enable it after the service pack is installed.

Source:Learn how to install Windows 7 Service Pack 1 (SP1)
Also read the one below: Installing SP1 using windows update (recommended)

Depending on your internet speed you should be done in about an hour.

If the download stalls, try it again. It took me two tries before it finished.

If you do get any errors document and report back.

No errors? Then double check your sleep settings allow the machine to go to sleep.

Re-awaken and see if you have sound.

Please post back to let us know how it went.

Here is your motherboard drivers direct from Gigabyte.
I would reinstall the Audio Drivers from there.
GIGABYTE - Motherboard - Socket AM3 - GA-MA74GMT-S2 (rev. 1.0)

Next I would run SFC \scannow to check file system

You could also try the Realtek High Definition Audio Codecs Drivers direct from Realtek site.
The latest version as of this post is R2.57

Windows Updates can have that affect on some machines.

The issue after "certain" updates may be corrected now that you have SP1 installed. windows can get "cranky" if it runs into improperly built drivers.

It may or may not. Just make sure the driver you are looking to download is newer than the one you already have.