Hey, I'm working on a lady's laptop and she has the Gateway MX6426 and I'm having the same issues. I've tried reinstalling windows, checked in the BIOS to make sure the audio is enabled, tried a different source for the file aside from getting it directly from Gateway and I'm still receiving failure as well. I'd be kinda odd for 2 laptops within warranty for the sound card to go. I'm not saying it's not possible but it is kinda weird. Maybe there's a different driver for MCE. On the website it says XP but there may be a difference. Are you running MCE as well?
MCE = Media Center Edition