It appears your rose 'Sterling Silver' blooms on new wood.* If you pruned late in the spring, and then pruned again before it set buds, you are probably pruning off the buds.* I found this info that might be helpful.
From what I've read on other boards and blogs, this rose is very unreliable over time.* Sometimes it does well for a few years and sometimes it never does well.* Everytime I read about it the main comment seems to be about this rose being a challenge.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.