Activate/Enable Sound in Windows 7 Safemode

Here are the sequence of steps. For full steps refer the reference [1].

1. Run (Win key+R key) regedit
2. Press Ctrl+F
1. Make sure "Keys", "Values", and "Data" are all selected
2. Type in Sound, video and game controllers
3. Click [Find Next]
3. Take note of the branch address in the status bar at the bottom (it will be something like HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4D36E96C-E325-11CE-BFC1-09002BE10318})
4. Copy the device-driver GUID (the long numeric part between braces) and paste it somewhere like Notepad
5. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network
6. Create a new key (right-click, select New → Key)
1. Copy the GUID you saved and paste it into the key name
2. Edit the (Default) value and type Sound, video and game controllers
7. Create several new keys (under Network) called AudioEndpointBuilder, MMCSS and Audiosrv
8. Edit the (Default) values of each of the new keys and type Service
9. Reboot (you’ll boot into safe-mode)
10. Open the Services snap-in (Win key+R key → services.msc)
1. Search for "Multimedia Class Scheduler", "Windows Audio Endpoint Builder", and "Windows Audio Service services", and check if they are automatically turned on (they should be). If not start them. 

References:
1. http://superuser.com/questions/354325/how-to-enable-audio-in-safe-mode