I'm not sure what you mean by your computer won't allow it. When you put the cursor over the Browse... button, click your mouse button. If you are still having trouble I would suggest using the Firefox browser.
Once you click on the Browse... button you can then find and select the picture you want to upload. It should be a gif or jpeg file, with the proper suffix at the end (.gif or .jpg) and the file needs to be less than 150 kb. Once selected the file name will show up next to the Browse... button. Submit the post, or click on add the file to upload another.
Hope that helps, but if you can fill me in as to what your computer won't allow I can look into it more.