Alright. So I tend to write information like math FORMULAS and instructions down. What I do is I write this all down into notepad and save the file as a .txt file in a folder. When I'm done with that, I delete the contents and move on to the next question.

However; I accidently made a mistake. After finally finishing a very long 4 PART series. I accidently hit save instead of save as. Because my process is me deleting the contents of the old notepad file and then doing this. What it did was overwrite the text instructions in the txt file instead of creating a new copy with the new instructions. I don't have file history turned on and I cant configure it. Is there anyway to get this old version back? It's highly important and I don't think I can write it out again. Don't close the file.
Now do the save as.
Next use the UNDO.
It is in the Edit menu.
Keep going back until you get the original text back.
Save it with a new name.
EDIT:
SORRY, just found out that Notepad has on one level of undo .

Next time, use a different tool that does auto backups for you. Or allows several files in one instance.
10 Free Notepad Replacements for Windows 7
Quote

NotepadTabs is a basic Notepad replacement which lets you view multiple text files in a single notepad and easily switch from one file to another through tabs at the top of the frame.

Don't close the file.
Now do the save as.
Next use the UNDO.
It is in the Edit menu.
Keep going back until you get the original text back.
Save it with a new name.
EDIT:
Sorry, just found out that Notepad has on one level of undo .

Next time, use a different tool that does auto backups for you. Or allows several files in one instance.
10 Free Notepad Replacements for Windows 7