Hi, i recently had a blue screen of death and i wasn't able to read the error message from the screen. When i restarted my computer my sound just died. All the drivers are working and nothing is muted. I tried disabling and enabling my Realtek Sound driver from Device Manager and i also uninstalled and reinstalled the driver but it didn't work. I Checked my Windows Audio Service and disabled and enabled it but that didn't work either. If i try to plug in a microphone or a headset into my computer it does not pick it up. I really don't know what is wrong as my the drivers are listed as working properly but there is no sound coming from my speakers or a headset that i plug in. Here are my specs.
Time of this report: 8/16/2012, 16:04:56

Operating System: Windows Vista™ Home Premium (6.0, Build 6001) Service Pack 1 (6001.vistasp1_gdr.080425-1930)
Language: English (Regional Setting: English)
System Manufacturer: Alienware
System Model: m15x
BIOS: PhoenixBIOS 4.0 Release 6.1
Processor: Intel(R) Core(TM)2 Duo CPU T8300 @ 2.40GHz (2 CPUs), ~2.4GHz
Memory: 2046MB RAM
Page File: 1930MB used, 2410MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 10
DX Setup Parameters: Not found
DxDiag Version: 6.00.6001.18000 64bit Unicode

Sound Devices
-------------
Description: Speakers (Realtek High Definition Audio)
Default Sound Playback: Yes
Default Voice Playback: Yes
Hardware ID: HDAUDIO\FUNC_01&VEN_10EC&DEV_0885&SUBSYS_152D0770&REV_1001
Manufacturer ID: 1
Product ID: 100
Type: WDM
Driver Name: RTKVHD64.sys
Driver Version: 6.00.0001.6662 (English)
Driver Attributes: Final Retail
WHQL Logo'd: Yes
Date and Size: 6/19/2012 16:54:20, 4065296 bytes
Other Files:
Driver Provider: Realtek Semiconductor Corp.
HW Accel Level: Basic
Cap Flags: 0xF1F
Min/Max Sample Rate: 100, 200000
Static/Strm HW Mix Bufs: 1, 0
Static/Strm HW 3D Bufs: 0, 0
HW Memory: 0
Voice Management: No
EAX(tm) 2.0 Listen/Src: No, No
I3DL2(tm) Listen/Src: No, No
Sensaura(tm) ZoomFX(tm): No

Description: Realtek Digital Output (Realtek High Definition Audio)
Default Sound Playback: No
Default Voice Playback: No
Hardware ID: HDAUDIO\FUNC_01&VEN_10EC&DEV_0885&SUBSYS_152D0770&REV_1001
Manufacturer ID: 1
Product ID: 100
Type: WDM
Driver Name: RTKVHD64.sys
Driver Version: 6.00.0001.6662 (English)
Driver Attributes: Final Retail
WHQL Logo'd: Yes
Date and Size: 6/19/2012 16:54:20, 4065296 bytes
Other Files:
Driver Provider: Realtek Semiconductor Corp.
HW Accel Level: Basic
Cap Flags: 0xF1F
Min/Max Sample Rate: 100, 200000
Static/Strm HW Mix Bufs: 1, 0
Static/Strm HW 3D Bufs: 0, 0
HW Memory: 0
Voice Management: No
EAX(tm) 2.0 Listen/Src: No, No
I3DL2(tm) Listen/Src: No, No
Sensaura(tm) ZoomFX(tm): No



---------------------
Sound Capture Devices
---------------------
Description: Digital Mic (Realtek High Definition Audio)
Default Sound Capture: Yes
Default Voice Capture: Yes
Driver Name: RTKVHD64.sys
Driver Version: 6.00.0001.6662 (English)
Driver Attributes: Final Retail
Date and Size: 6/19/2012 16:54:20, 4065296 bytes
Cap Flags: 0x1
Format Flags: 0xFFFFF

Description: Stereo Mix (Realtek High Definition Audio)
Default Sound Capture: No
Default Voice Capture: No
Driver Name: RTKVHD64.sys
Driver Version: 6.00.0001.6662 (English)
Driver Attributes: Final Retail
Date and Size: 6/19/2012 16:54:20, 4065296 bytes
Cap Flags: 0x1
Format Flags: 0xFFFFF

DxDiag Notes
------------
Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Sound Tab 2: No problems found.
Input Tab: No problems found.

There are no errors in device manager under sound, it says all the drivers are working properly

This might be due to the blue screen. That blue screen comes when the system file crashes and also when Windows crashes. Most probably the device drivers has been corrupted and you need to re install the driver for that. If doesn't help, you try repairing the Windows installation.