Maybe the browser was accidentally disabled auto-detection of encoding. Try to turn it on. To do this, select the menu item "View" - "Encoding" (in older versions of Opera and many other browsers), or "Page" - "Encoding" (in the new versions of Opera). Switch mode, which can be called "Automatically" or "Choose automatically". Maybe the text on the page will immediately become readable.
If the page display was not normal, find the correct encoding manually. To do this, go to the same menu item as in the previous case, but instead of the automatic mode select the coding KOI-8R - for sitex, created before the transition to Unicode, it is the most common. If it fails try the same method to choose the encoding CP1251, CP866, and if does not help and it pereproshit all the standards were from the category "Cyrillic".
Information about the encoding of the page is typically stored in its source code, and it is on the basis of these data it determines the browser. To read the source code of the page, click on the menu, depending on the browser, select "View" - "Source code" or "Page" - "development Tools" - "Source code". In the beginning of the text locate the following line:meta http-equiv="Content-Type" content="text/html; charset=encodingname" where encodingname - the name of the encoding. Then select in the browser menu this encoding.
Standard browser tools powerless, if you use a less common encoding, or the text was subjected to multiple transcoding. To decrypt it, go to online decoder, for example, http://www.artlebedev.ru/tools/decoder/. Place a piece of text from the page in the input box and click "Decrypt". To do this, select the text with the mouse, press Ctrl+C click in the input box and hit Ctrl+V. In the case of success together with the decrypted text you will receive information about what encoding it was.