If the water level inside the tank is lower than the outlet pipe, chances are you have a clogged or broken pipe between the septic system and your house. This is a pretty common repair that can sometimes be as simple as calling a plumber. 

Soppy soil between the house and your septic tank is generally a pretty good sign of a broken pipe. Sometimes this can be tree roots or simply decaying pipes, or perhaps you were digging in the area. While not as simple as a pump-out, this is generally a fairly straight forward fix.

Aerobic Treatment Units aerate the tank to help break down waste faster. If you've been away for a long period of time, the good bacteria that helps your tank work may have simply died off. Generally, using your tank sparingly for a couple weeks will help the bacteria grow back to usable levels.

Unfortunately, drainage/leaching field failure is not generally a "fixable" problem. Most often, failure of the tank from not being pumped out often enough causes semi-solid waste to accumulate and clog up your leaching/drainage field. When this happens, your field can no longer drain effectively and will need to be replaced in part or in full.