Audio playback problem in win 7

Hi GUYS....,

my pc info is:

WINDOWS 7 32 BIT (SP1)
CORE I3 540 3.07 Ghz
BIOSTAR H55 HD
1TB
4GB MEMORY

no sound card
no separate GRAPHICS card (onboard 64 MB)

DFX VER 11.1 INSTALLED

Problem: less than one month installed win7 (SP1)with all working fine till last 10 days...
no audio playback, video playing. when googled, i got one option...control panel..trouble shooting..audio playback..(two options, 1. DFX and 2. Speakers (Realtek hd audio)..i chose "speakers"..then "change selected audio device to default...."..."apply this fix" (applied)..then only it worked. but every time i start my PC, and play some audio/video, there is no sound (audio playback) except video. again i have to go the same long trouble shooting steps (everytime i start my PC!)

i uninstalled Realtek audio driver and re-installed and updated it, (windows updates are upto date every time, but the problem persists even today, please help me Guys.

Thanks in advance.

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