“Can't connect” is vague. Rule things out in this order and you'll locate almost any problem.

1. Did the core start?

Check the log at the bottom of the main window. Repeated failed to start or no log at all usually means the core is missing or quarantined by antivirus. First update the core and whitelist the v2rayN folder in your antivirus.

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2. Is the node itself alive?

Right-click the node → test real-connection latency. A timeout means the node or route is dead — switch nodes or refresh the subscription. Don't waste time on a bad node.

3. Is the system proxy on?

Right-click the tray icon and confirm it's “Auto-configure system proxy”, not “Clear system proxy”. Browser extensions like SwitchyOmega can override the system proxy too — disable them when in conflict.

4. Protocol issues

REALITY / Vision but no connection: make sure the core is Xray. Using VMess: check the PC clock is accurate, within 90 seconds.

5. Port in use

Log says address already in use: change the local listen port (default 10808/10809) or kill the process holding it.

A quick split: latency tests fine but the browser won't load → system-proxy/routing issue; latency test itself times out → node or core issue.