When you first turn the game on, there is a relay, a few coils, and a motor or two on the 50V line that could be problematic.
I'd start by isolating the issue. If you unplug the playfield jones plugs, does the fuse still blow when you turn it on? If so then your shutter motor is likely at fault.
If not, then the job gets harder, but hopefully not by much (you can plug the playfield back in at this point). The simple stuff is the stuff that's always active when you turn a game off and back on - the replay reset relay and the replay register. Set your credits manually to zero if they are not already there, and then try again.
If the fuse blows, there's one more simple thing to check - have all the balls lifted? The lifter motor may have shorted. If not, it gets considerably harder. But there's other stuff to try and a few likely suspects. Report back.
If, on the other hand, your problem is when you hit the start button and not when you turn the game itself on, let us know that too.