I assume you checked the power with a multi metre ?
I would firstly make sure the battery IS fully charged by charging it, don't rely on a reading as it takes no "power" as such to operate a metre.
The best way to test a starter is to hook it up to a supply on the output side of the solenoid first to see if the actual motor is going, as most are just jammed solenoid's, esp if they are BOSCH.
I have just done a escort diesel van, brand new heavy duty battery brand new starter, (old ones brushes were so worn they fell out of the brush box!!) all connected just a clunk, sometimes nothing, metre showed full value, no particular resistance etc.
So bolted my test lead(one I made up) to the battery direct, then touched the solenoid and bingo burst into life, seems even the solenoid needs a good kick power wise, most are just stuck so a good clout usually frees them.
Looked at connection points, was the solenoid lead where someone had repaired it badly, but used heat sink to cover the worst crimp joint I have ever seen, resoldered a new terminal on there, hasn't missed a beat since, so just the two timing belts to do now and the tappets(shims)!!
As one of me mates says, "if in doubt give it a clout", reffering to the starter.
tabetha