The problem with the quest \"tower Defense\" (Fallout 4)

Hello, there is a problem with the quest tower Defense
Came to Preston after first arriving at the Institute,handed over the quest, and Preston said the castle needs your help and I got the quest tower Defense
I came to the castle, talked to Ronnie, after that I gave a few moments for the construction of protective structures, came the first wave of synths...
Synths came only once, a small group, quickly interrupted them and everything, more nothing happened, no synths were coming and progress of this fragment of the task remained at 0%
Fallout net, took place without a console and other slobodov, at the time of issuance of the quest was level 21, now the 25th (so all bad)
If you know what the problem is, please inform what it is and its solution.

For earlier thanks!