Sound problem with intro movies of games

I did a search and I did not find this question previously asked.

I recently formatted my hard drive and reloaded the programs, however now the intro movies to games (such as oblivion, Doom3, WOW, and Prince of Persia) keeps skipping, i.e the sound goes in and out. I checked my direct X version but it is up to date. I checked the drivers and there are no conflicts (i.e exclamation points, or question marks) for the video or audio.

System Manufacturer - Clevo
System Model - D900K
Processor - AMD Athelon 64 X2 Duel Core Processor 4200+ MMX 3DNW (2CPU's)
Memory - 2046 MB RAM
Display Adapter - NVIDIA GEFORCE GO 7800 GTX
Sound - RealTek AC97 Audio

When I tried to update the NVIDIA drivers the program asks me for an NVIDIA windows disk during the update but I dont recall ever having an NVIDIA disk (perhaps it is with another installation disk?).

The sound plays fine during the actual games and music (dvds and cds) play fine also.

Any help anyone can be would be greatly appreciated,