I've had the same springs in for about ten years, so I don't think they lose their stretch very quickly.
How many springs are you using? I use three, and I'm using stainless 9's, tuned to e flat. For standard tuning I run pretty close to the top of the spring travel, but three works.
If you add another spring, you'll be able to loosen the screws.
If your tremolo won't accommodate more springs, maybe they ARE sprung. If you remove the spring, it should compress all the way, so that the winds are touching. If they don't, maybe the spring has been over-extended. If so, you need new ones.