Suddenly, no sound on my Toshiba Satellite M55-S325

[xpect2win]

Hi!
I was watching a movie on DVD when suddenly I lost all sound from my Toshiba Satellite M55-S325. There are no error messages. I did all the normal checking volume settings, making sure nothing was muted, checked audio drivers. No errors or (!) on device manager. Everything appears to be working correctly just no sound coming out of speakers or headphone jacks. No system sounds. No sound at all. If I play a song using itunes or windows media player it plays the song with no errors and appears to be playing it from the audio bars at the bottom. Just no sound comes out. I used system restore to try several different restore points where I knew the sound previously worked. Still no sound. (By the way, It had happened once before too while watching a movie. I had tried system restore, initially it didn't correct and then after one restore the sound came back)
I also found that my system was affected with virus (carried through my JetFlash)- Brontok. Thereafter the system restore feature, on even Task Manager had stopped working (I'm not sure if this happened after the virus affected my system). I did a FULL SYSTEM RECOVERY, and installed an anti-virus and updated it. I've updated Realtek AC'97 driver, re-installed it from the original disk too.
I'm not sure what all details you need and where I'd get those from, so I'd appreciate directions. Giving some details below.
PLEASE HELP!

OS Name Microsoft Windows XP Home Edition
Version 5.1.2600 Service Pack 2 Build 2600
OS Manufacturer Microsoft Corporation
System Name GYANENDRA
System Manufacturer TOSHIBA
System Model Satellite M55
System Type X86-based PC
Processor x86 Family 6 Model 13 Stepping 8 GenuineIntel ~1728 Mhz
BIOS Version/Date TOSHIBA V1.30, 04/07/05
SMBIOS Version 2.34
Windows Directory C:\WINDOWS
System Directory C:\WINDOWS\system32
Boot Device \Device\HarddiskVolume1
Locale United Kingdom
Hardware Abstraction Layer Version = "5.1.2600.2562 (xpsp.040919-1030)"
User Name GYANENDRA\Mokan
Time Zone India Standard Time
Total Physical Memory 512.00 MB
Available Physical Memory 49.59 MB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 1.20 GB
Page File C:\pagefile.sys