You hear sound without the IDT driver because Vista has installed its own Intel HD audio driver which provides basic sound. When you try to install the IDT HD audio driver the installation fails, so there is no audio driver and so no audio.

This is hard to diagnose without knowing the complete history. When you received your computer it should have had the IDT HD audio driver pre-installed. It would be helpful to know why and when it was uninstalled, and if there was an operating system reinstallation involved.

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Did the mute problem occur before you first tried to install the Creative software or afterward? The reason I ask is that sometimes if you have a failed attempt to install the Creative software while the IDT is not installed, that can cause a failure of Windows Audio Service. You are seeing error messages about the Service so this is the first thing I would check. Go to Start/Run and type "services.msc" then hit the 'Enter' key (or click 'ok'). The Services window will appear. Scroll down until you find "Windows Audio" towards the bottom of the list. Check that it is enabled, set to automatic, and running. If it isn't, double click on it and change the Startup type to Automatic, then click Start, Apply, and OK. If it will not start and gives you an error about "dependencies" or "Windows Audio Endpoint Builder ", then do this:

Create a System Restore point, then Go to Start>Run and type regedit to open the Registry editor. Navigate to

HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Audiosrv

and in the DependOnService remove all entries except RpcSs and then restart your computer. Check to see if the Audio Service is running.

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If you get the Audio Service running then next you have to reinstall the IDT audio driver. If you still get the error "no audio device is installed" then try this: Go to the Studio 1555 downloads page and install in this order:

a. Dell Notebook System Software (on your downloads page expand the System Utilities category). Restart.

b. Next install the Intel Chipset software (expand the Chipset category). Restart.

c. Install the IDT audio driver (expand the Audio category).

The Notebook System Software and particularly the Intel Chipset are needed for the system to be able to detect the audio device.

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If these steps do not resolve the problem then consider using Factory Image Restore (see page 40 of the Setup Guide) to undo the errors in the current configuration of your computer.

I have a similar problem - My Studio 1555 : Pentium Dual Core T4300(2.1GHz,800MHz,1MB) crashed and had to have a new Mother Board. (it  froze and had buzzing inside) The service eng came out and put in a new board. 1 hour later the sound has now disappeared and laptop says "No audio driver is installed". The Op system in Windows 7  - I paid extra for Creative SoundBlaster Xfi MB Software Suite. Also the INternet connection has gone down (my other PC connects - it is the laptop at fault)  I am going nuts!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Never again! Also the support is not open at weekends so will have to wait till Monday. Any ideas???? Bill