I'm not sure I understand the problem. You are trying to blur the image using Gaussian Blur and you entered in the little box a (whopping) 4,768 pixels. Then you pressed ok and your computer froze? Or actually it seems that the image became so blurred that you couldn't see anything at all?

In either case, don't blur something by 4,768 pixels at once. Instead, try blurring it 500px and see how that looks, then repeat as necessary. I had a look at RoB A's very good tutorial, and he just says (in post 6) that you need to Apply a Gaussian Blur (Filter->Blue->Gaussian Blur) large enough to eliminate the absolute black and whites of the image. So do 500px once, then again if that was not enough, and so on until you have a nice smooth image full of greys.