(quoted from post at 15:20:01 09/12/15) Since you've already done the usual things, check the unusual...
Make sure the engine is free to turn. Try holding the clutch down, that will take the transmission out of
the equation. Are all the belt driven accessories free turning? Are all the hydraulic levers in the center
position? If this is a diesel, were the proper amp rating battery installed and the proper size battery
cables used?
If all checks out, you'll need an analog volt meter to check the electrical system under load.
Start at the battery posts, directly on the posts, not the cable ends.
Take the reading with no load. Should be around 12 to 13v.
Hit the starter, take a reading while cranking. Read the low point as the starter brings the engine through
each compression stroke.
If the volts stay up around 11-12v, the power is not getting to the starter, or the starter has an
internal problem.
Start systematically moving the test leads toward the starter, taking under load readings until
you find the point where the voltage drops significantly. (Hint: As you are testing, feel for hot
connections. If it's getting hot, there is a problem.) Remember, you are not just checking cable
connections. A proper ground connection between the battery and chassis is critical, as well as a ground
between the starter case and the engine. Don't forget to check for voltage drop across the solenoid. If
your final test point is between the starter post and the starter case, and the voltage is still high, the
starter is bad.
If the battery post voltage drops below around 8-9v, the battery could be bad/discharged, the starter
is dragging/shorted internally, or the engine is binding and too hard to turn.
If the battery cables jump or heat up (and they are the proper size or bigger), the battery is
doing it's job and something is causing too much amp draw. This is typically caused by bad starter bushings
or the engine is bound, too hard to turn.