ATVConnection.com ATV Enthusiast Community - 85 250 transmission problem! PLEASE HELP

I was riding yesterday, on 5th gear on a gravel road, and then my 85 big red 250 made a loud sound and coasted to a stop. When I hit the starter, it makes a click sound but nothing turns. The kick start doesn't even move. When I shift it into gear, I can move the wheel in reverse with resistance, but it doesn't even budge trying to turn it forward. I opened on the left side and checked the starter gears, and they are in perfect condition. Would this mean that somewhere in the center my gears are locked up, thus I'm not able to move the tires forward? My friends brother might fix it for me if he has some time, but if not, would this be something I could do myself with a repair manual. I've never opened up a motor before, but I've taken apart everything else on my machine before. My friend I would have to split the block, and I should see the problem right their. I don't want to spend a lot of money on it a shop to get fixed, that' s why I want to do it myself. Although, how much you think would it cost to fix this problem? Thank you! PLEASE RESPOND!

JasonJ