diff --git a/app.go b/app.go
index a144d4d..066372d 100644
--- a/app.go
+++ b/app.go
@@ -997,6 +997,7 @@ func (a *App) startup(ctx context.Context) {
 	// One line in the startup log too, not only in OpsLog's own: the two
 	// together say whether a launch that produced no window got as far as our
 	// code at all, which is the fork every "it does not start" report turns on.
+	startupReached.Store(true)
 	bootLog("OnStartup reached")
 
 	dataDir, err := userDataDir()
diff --git a/bootlog.go b/bootlog.go
index 26bcbf3..80711d1 100644
--- a/bootlog.go
+++ b/bootlog.go
@@ -19,6 +19,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync/atomic"
 	"time"
 )
 
@@ -93,3 +94,18 @@ func checkDataDirWritable() error {
 	bootLog("data dir ok: %s", dir)
 	return nil
 }
+
+// startupReached flips as soon as OnStartup runs — the first moment OpsLog's
+// own code is executing inside the window's lifecycle.
+var startupReached atomic.Bool
+
+// startupStuckMessage is what an operator sees when the window never starts.
+//
+// It names the two causes and what to do about each, because "OpsLog is not
+// responding" sends people to reinstall OpsLog, which is the one thing that
+// cannot help: the part that has not started is not ours.
+const startupStuckMessage = "OpsLog started but its window never opened.\n\n" +
+	"This is the WebView2 runtime failing to start, and it is almost always one of two things:\n\n" +
+	"• The Microsoft Edge WebView2 Runtime is missing — install it from Microsoft, then start OpsLog again.\n" +
+	"• An antivirus is blocking msedgewebview2.exe — add OpsLog's folder to its exceptions.\n\n" +
+	"The details are in the OpsLog folder under LOCALAPPDATA (startup.log)."
diff --git a/main.go b/main.go
index 96f5215..8041dc0 100644
--- a/main.go
+++ b/main.go
@@ -145,6 +145,23 @@ func main() {
 	}
 
 	// Create application with options
+	// A HANG has no error to report, and that is the shape being chased here:
+	// the process stays up, the data folder is created and stays empty, and no
+	// window appears — WebView2 never finishes creating its environment, and
+	// nothing returns to be logged.
+	//
+	// So the absence of progress is what gets reported. If OnStartup has not
+	// been reached a few seconds in, this says so and names the two things that
+	// cause it, rather than leaving an operator watching a process that is doing
+	// nothing at all.
+	go func() {
+		time.Sleep(12 * time.Second)
+		if startupReached.Load() {
+			return
+		}
+		bootLog("STUCK: 12 s after wails.Run and the window has not started — WebView2 never handed control back")
+		fatalBox("OpsLog", startupStuckMessage)
+	}()
 	bootLog("entering wails.Run (window %dx%d, state %v)", width, height, startState)
 	err := wails.Run(&options.App{
 		Title:            "OpsLog",