There are two ways to approach HDR in Photoshop now. One way, of course, is you can use the Merge to HDR Pro feature to combine several photos into an HDR image. However if you are after that HDR look on a photo that wasn’t shot for it. Go under the Image menu to Adjustments and choose HDR Toning. Here you have a number of settings that, when manipulated, can yield a pretty convincing HDR looking form one photo. Hence the name: HDR Toning. It’s worth exploring because I have discovered that with some experimentation the results can be very interesting.