inspiron 6400 modem device on high definition audio bus ?

under my device manager i have a question mark next to modem device on high definition audio bus. I went to the dell website and downloaded all the drivers availible for my service tag, but this message is still there. i downloaded the sigmatel driver that was listed but im not sure if it installed correctly. Also, when i scroll up and down in internet explorer its very eratic, not a smooth motion like it used to be. does this have something to do with the video drivers?