No there is no such cable, and no there is no way to make one, because HDMI is a digital signal, and those 3.5mm cables are analog. You'd need some kind of a conversion device.
Also, in order to get 5.1 sound, you need an audio source that has 6 discreet channels of audio in it, such as a DVD movie. Or you need some kind of program, or bit of hardware, that will do audio upmixing. Without that, if you only have a stereo signal, it's perfectly natural for you to only get left and right speakers going.
As someone who was in a similar position as you maybe 6-7 years ago, take it from me, just go out and get a home theater system. That is where you'll end up anyway. Multi-channel computer speaker systems are a waste of money, because you're never going to get them to work how you want. It's simply not going to happen. Computer speakers also tend to have rather horrible frequency response ranges, which will dramatically affect the quality of the audio.
Save yourself a lot of time and effort, just buy a home theater system with some speakers that are actually worth something. The bigger the frequency range supported by the speakers the better, and by and large, the bigger the better. Usually bigger speakers have better frequency ranges at cheaper prices. You can get smaller speakers with high frequency ranges, but you'll pay a pretty penny for them. And you also want a powered sub. Trust me, there's no comparison between the two, and a sub has a rather dramatic impact on the depth of the sound you get.
You don't need to buy some $10,000 home theater system, just look for the best you can afford. And I'd also suggest buying a refurb unit for your first go. Onkyo has their Club Onkyo site which routinely has refurb stuff. I've bought a few things from there, and honestly, they both came looking as if they were brand new. I think a lot of Onkyo's refurbs are actually discontinued models they're trying to clear out. So if you don't mind that, you can save a couple hundred bucks. Be a good way to kind of get your feet wet in the wide world of home theater equipment without a massive cash outlay. Once you get the hang of things, you can start looking for a better receiver and/or speakers. Just stop wasting your time with computer speakers, because they will absolutely never do what you want.
Okay what I want to do is connect my hdmi to my Logitech COUMPUTER speakers right now I have all three 3.5mm stereo plugs going into my headphones port on my COUMPUTER with this set up I have no 5.1 sound. I was told that the hdmi would give me the sound I want out of my speakers is this even possible is there such thing as a hdmi on one end and the other end of the plug a 3.5mm plug and if not can you make one? Thanks