Apparently not getting enough voltage to the starter (assuming it's not the
starter).  Could be the battery, dirty, corroded battery connections, loose
connection at the starter terminals, etc.  One way to help pin your problem
down is to get a good check of your battery.   It's a standard test where
they load the heck out of it and it has to be able to maintain voltage and
current requirements.  Just tell the shop you're not sure if you need a
battery and if it can be checked out.  Then there is the starting system
check--You need one of these because one night when you're out in the
boondocks it won't start at all.
MLD