Trying to hook up a pc to a tv

[The Last Ancient]

Ok, not sure where to post this, but hopefully there are more tech savvy people on this forum then I am. Basically I'm trying to hook up my mom's new hp computer to her fairly new samsung hdtv.

I bought a dvi to hdmi cable and that successfully put the picture on the tv but without sound.

I am looking for what exactly the correct sound cable is for the computer. I think its a 3.5mm something or another but this is where it gets too techy for me. It needs to be 15 feet or so.

I also noticed that there is another spot, labeled pc on the back of the hdtv. This is not the hdmi port where I am plugging my dvi to hdmi cable. I wondered if there is a better cable I could get, a dvi to whatever the hell that slot is on the back of the tv, that would hopefully transfer sound as well.

My mom wants to stream netflix and doesn't have a device downstairs and doesn't want to watch it on the computer, hence my predicament. Any help would be much appreciated as I am tired of trying to figure it out, thank you.