texstudio- cyrillic shows up garbled or like question marks

Question

EDIT: going to the options menu, going to the editor section and changing the font enconding from UTF-8 to windows- 1251 fixed the problem thanks, daevid

I'm extremely new to this, having started using TexStudio for an urgent matter since last week and have had no previous experience, prior knowledge or anything like that go off of, so please be patient.

So I have a set of files that I've set up to compile together into one file. Some are at least 5- 6 years old, others I've made in the past few days, the language on them is the same, that being Bulgarian.

The text on some of the old files is seemingly garbled, like this

"Äèñåðòàöèÿòà ñå ñúñòîè îò ïåò ãëàâè - óâîäíà ãëàâà, òðè ãëàâè ïî ñúùåñòâî è çàêëþ÷åíèå. Ïúðâà ãëàâà ñå ñúñòîè îò òðè ÷àñòè, êàêòî ñëåäâà"

However, when texstudio builds a pdf out of it, the text shows up fine on the built PDF. If I try to add any more words to it, the words are displayed as question marks. Symbols are fine, numbers are fine, english text is fine, but cyrillic is broken. This problem also shows up for the bibliography as well.

The old files that don't have this problem seem to work and look fine with no garbled text and when i add anything new to them, the text doesn't show up as question marks.

I've also seen mentions of a "biblatex" when i tried to install it using miktex, it still didn't pop up in texstudio.

Changing the encoding to UTF-8 did not yield any results, as the text still showed up all the same.

Now I do have one main file that contains all the definitions, set up like this

\usepackage{amsmath,amssymb,latexsym}
\usepackage[T2A]{fontenc}
\usepackage[cp1251]{inputenc}
\usepackage[bulgarian, english]{babel}
\usepackage{mathrsfs}
\usepackage{amsthm}
\bibliographystyle{plain}

\usepackage[cp1251]{inputenc}
\usepackage[T2A]{fontenc}
\usepackage[english,bulgarian]{babel}
\usepackage{subcaption}

\usepackage{graphicx}
\usepackage{epsfig}

\usepackage{latexsym,amsfonts,amsmath}
\usepackage[cp1251]{inputenc}
\usepackage[T2A]{fontenc}
\usepackage[english,bulgarian]{babel}

\usepackage{graphicx}
\usepackage{epsfig}

Also thinking that maybe the version of TexStudio that I was using was outdated, I updated it from 4.1.3 to 4.2.3, that however only ended up causing more damage as one of the files is now all question marks. Not just the output, but the text in the file itself as well.