Sounds like a memory issue. How old is this PC? RAM? Why don't you just do the offer and get a free Roku Stick? I know it runs fine on those. I have it on two older Rokus.
I built it last year 8 Gb Ram, i5, GTX770. Sling works great everywhere but my PC. I did the offer for the free Kindle Fire stick for signing up for three months. Works great on my tv.