diff --git a/gns3server/controller/compute.py b/gns3server/controller/compute.py
index 65bca3c34..9a9d94c29 100644
--- a/gns3server/controller/compute.py
+++ b/gns3server/controller/compute.py
@@ -375,6 +375,11 @@ class Compute:
                 log.info(f"Connecting to compute '{self._id}'")
                 response = await self._run_http_query("GET", "/capabilities")
             except ComputeError as e:
+                # Update connection status and notify UI
+                self._connected = False
+                self._last_error = str(e)
+                self._controller.notification.controller_emit("compute.updated", self.asdict())
+
                 if report_failed_connection:
                     raise
                 log.warning(f"Cannot connect to compute '{self._id}': {e}")
diff --git a/gns3server/controller/project.py b/gns3server/controller/project.py
index 8d8eeebee..cab967a99 100644
--- a/gns3server/controller/project.py
+++ b/gns3server/controller/project.py
@@ -1029,6 +1029,29 @@ class Project:
             except ControllerError as e:
                 # ignore missing images or other conflicts when deleting a project
                 log.warning(f"Conflict while deleting project: {e}")
+
+        # Check if all computes used by this project are connected before deletion
+        # We need to check from the topology file because _project_created_on_compute
+        # gets reset during open()
+        disconnected_computes = []
+        for compute_id in self._computes:
+            try:
+                compute = self._controller.get_compute(compute_id)
+                if not compute.connected:
+                    disconnected_computes.append(compute)
+            except ControllerError:
+                # Compute doesn't exist anymore, consider it disconnected
+                log.warning(f"Compute '{compute_id}' not found in controller")
+                # We can't add it to disconnected_computes without the compute object
+                pass
+
+        if disconnected_computes:
+            compute_names = ", ".join([f"'{c.name}'" for c in disconnected_computes])
+            raise ControllerForbiddenError(
+                f"Cannot delete project '{self.name}': {len(disconnected_computes)} compute(s) are disconnected: {compute_names}. "
+                f"Please fix the connection or delete the project manually on those computes."
+            )
+
         await self.delete_on_computes()
         await self.close()