Look in your Windows Firewall for BOINC entries. Is the Home Network Group ticked or also the Public? The art is if things in Firewalls are messed up is to exit the troubling program and delete all the related rules in the firewall. Start the troubled program and let the Firewall warnings pop up... then read them, before deciding. I've set up an extra port+IP rule so BOINC can talk to the project server that I choose BOINC to be allowed to talk to. That's done in Advanced Rules, Incoming/Outgoing connections. Under incoming I found 10 auto-permitted rules for BOINC and BOINC Manager.

But, what version of BOINC did you install. As Service + All user? At least I've had no issues.