If the engine will not crank over, the most common problem is the starter. These will tend to go out at about 100,00-125,000 miles. Sometimes it is only the starter solenoid, but often the complete starter (including solenoid) needs to be replaced.Google+
Car Problem Reports
Toyota 4Runner Vehicle Won't Crank Due To Starter
Toyota 4Runner Problem
Average Mileage: 153,814 mi (66,700 mi - 234,000 mi)
Visitor, 1990 Toyota 4Runner, 200,000 mi
Had the same problem with my 4runner. Don't replace your starter if you can have it refurbished; it's half the cost of a new one + the original starters are of better quality than new ones and will last way longer and you get one back to new-like condition with all-new solenoids, etc...
Visitor, 2005 Toyota 4Runner, 107,000 mi
Click, click, click... engine will not turn over. Starter failed/failing.
Visitor, 1996 Toyota 4Runner, 141,000 mi
The engine will start intermittently but the starter needs to be replaced.
starter seemed to be frozen, beat the crap out of it with a pole... it hasn't stopped working yet
Visitor, 1997 Toyota 4Runner, 130,000 mi
engine will not turn over to start car
Visitor, 2005 Toyota 4Runner, 66,700 mi
Intermittent starting. Vehicle would take several times to crank, no clicking sounds at all. Battery, ignition and alternator all okay. Replaced starter because of corroded contacts and corrosion on/in starter.