1995 S10 Chevy Blazer tranny issue
 

I have a 1995 Chevy Blazer that will not go into reverse. It has a 180K on it and has not been moved in months. I want to get it going for use as a beach driving vehicle. I'm assuming that its the transmission but I was told that it could be a switch or sensor and that the truck could not be going into reverse because of that. Any input would be greatly appreciated.