Scratchy Sound Problem

Hello everyone,

I have MSI K7N2 Delta Series mainboard with Nvidia Nforce on-board sound card. Sometimes , for ex ; while playing Mp3's , music accelerating itself , fastening like someone adjusted it's playing speed.

However , while playing Doom 3 ; sound sometimes repeating itself ; for ex , last word repeating for 3-4 times. And very oftenly scratchy sound appears.

I have downloaded direct x 9.c ; but while in 9 b it's again scratchy. And I have the latest nvidia nforce sound drivers...

Then I plug in a Creative 5.1 digital sound card. Again scratchy and repeating sound appears.

I decide to format my system , but is there any other solution? What do you think about my problem? I fear if it will stand still after format! Also my some videos playing twisted , upper side goes down. I think my some video and sound codecs are wrong.