At the same time you weren’t able to add Plots and to use Plots (this thread). the first issue is solved and I think the two issues are related and, in general, not a Plots.jl issue.
Maybe its best to remove Julia and start over with a new clean install: Deinstall Julia and remove folder C:\Users\a225\.julia
As a beginner of Julia, I found it is quite frustrating for this type of bugs.
Please try to communicate more open, it helps to find solutions and to help you. I understand that you are frustrated if things doesn’t work smoothly but, as a beginner, you are possibly not the one to decide what a bug is and for me it seems, that the problems you have, derive from your Windows 7 system, which is not in the best state (despite that it is a massive security thread for your own personal data).
I say that because you are talking about bugs in Plots.jl AFTER you got the solution in the other thread (which, by the way, maybe still uncomplete).
In general you should upgrade to Windows 10 (if possible). It is still free, e.g. https://www.howtogeek.com/509087/how-to-upgrade-from-windows-7-to-windows-10-for-free/