how to open the wallet in the text editor?
Simply right click the wallet file, select "Open with" and choose the Notepad or any other text editor.
But please, answer my other questions. Search for the address on the blockexplorer to see if the balance is there and tell me how the addresses look like before (right now on your Electrum) and after the import with the private-key.
Yes I checked in the Blockchain and it's empty. I opened the file in the text editor but I did not find anything seed or xprv.