Just bridge the solenoid terminals to make sure the motor part is not jammed, this will not engage the starter merely cause it to spin, the ngagement part being done prior to spinning by the solenoid.
As it was working before chances are it is fine, so you need to find why it is not getting enough oompf from the battery, or cable problem.
Did you reconnect the starter wire that has a disconnet terminal near the battery, about 6" away a thinner wire ?
tabetha