If you have a TGraph, SetRangeUser will not work for the x axis.

TGraph* myGraph = new TGraph();
...
myGraph->SetRangeUser(lower,upper);

will not complain but also not do anything. Or not the thing you want.

You have to use SetLimits(), like:

TGraph* myGraph = new TGraph();
...
myGraph->SetLimits(lower,upper);