Well, what I want to know is if you USED to have sound or not. If you never had it, and this is your last piece of the puzzle, then all you probably need is drivers.
If it used to work and now it stopped, and you get boot up problems, then something probably got corrupted on the hard drive.
I'd start by booting 2 or 3 times to see if the problem "goes away".
If it doesn't, a scan of the HD would be good, or even try a reformat and fresh OS install I guess. All depends on how much stuff you have on your HD that you don't want to lose. If there's nothing you care about, then go for a format.