How do I check a Ranger XLT Transmission?

My Ford Ranger is a 1989, 5 speed manual transmission. I seems to have "locked" in some gear or gears. When I let the clutch out, the engine pulls down as if I the brake is depressed. The truck tries to move but does not. I cannot get it into any gear expect reverse and 5th. I know little or nothing about transmissions (very little about cars). Suggestions? Thanks.