Can no longer shift to lowest gear
This sounds like a situation where you should have a professional bike mechanic look at the problem.  If you have attempted to resolve the problem by adjusting both the correct limit screw (you did make sure you were adjusting the correct limit screw, right?) and the indexing via the barrel adjuster, then something else is wrong.  One possibility is that your derailleur hanger is bent, although without seeing it I could not say that is the problem for sure.  Whatever the issue is, if you can't find it yourself, you'd be best served by pulling in some additional help rather than floundering and potentially throwing everything else out of whack.