It is possible to make sound work on Safe Mode.
- Press Windows + R, type devmgmt.msc, press Enter and look for your sound device. (e.g. Reatlek High Definition Audio) Double-click it.
- Go to the tab 'Details' and click the drop-down list. Select 'Driver key' and copy the text from 'Value'
- Copy the text into a Word processor (e.g. Notepad)
- Replace all lower-case letters with capital letters and remove the \0000.
- Open Registry Editor (Windows + R > regedit) and locate HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network.
- Create a new key (Rightclick > New > Key)
- Copy the text from your Word processor and paste it into the key name.
- Edit the '(Default)' key and type 'Sound, video and game controllers'.
- Create a new key called 'AudioEndpointBuilder', 'MMCSS' and 'AudiOSrv'
- Edit all their '(Default)' keys and type 'Service'.
- Restart your computer
- Go to Services (Windows + R > services.msc) and start Multimedia Class Scheduler and Windows Audio Endpoint Builder.
- Then start Windows Audio Service
This has been tested and functioning properly on an Acer Aspire desktop. This workaround may not work with Windows XP.