I would check your battery voltage first.  A totally dead battery or one with
a bad cell won't work even with a jump start.

The second thing to try if the battery is good, is to try the ignition while
someone checks to see if there is voltage back at the solenoid with a
multimeter.  This tells you if you have a starter problem or a ignition
switch problem.  If you have juice to the solenoid wire then your solenoid is
bad.  You could try jumping the solenoid terminal to the starter power
terminal with a screw driver too if you don't have a meter.  If the starter
cranks over then the switch is bad.

The third thing to try is to have someone hold the ignition on and to tap the
solenoid on the starter with a hammer (or a metal bar).  We have done this
with sticky starters before and it will work.  If this works then the
solenoid is bad and you should just get a rebuilt starter.

Here is a list of parts available from Van-Again if you need them:
Rebuilt Starter $135 with a $60 core charge (Bosch)
Ignition Switch- $8

Hope this helps,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242