diff --git a/PCL.Core/App/Localization/Languages/en-US.xaml b/PCL.Core/App/Localization/Languages/en-US.xaml
index 43250bafb..2c001c31c 100644
--- a/PCL.Core/App/Localization/Languages/en-US.xaml
+++ b/PCL.Core/App/Localization/Languages/en-US.xaml
@@ -799,6 +799,7 @@
     <sys:String x:Key="Instance.Install.NoExtraInstall">No extra installation</sys:String>
     <sys:String x:Key="Instance.Install.Reset.Message">You are resetting the current instance.&#xA;PCL CE will re-download the files required for this instance from the internet and reinstall mod loaders (if any).&#xA;This operation will not lose your saves, mods, resource packs, etc.</sys:String>
     <sys:String x:Key="Instance.Install.Reset.Title">Reset this instance</sys:String>
+    <sys:String x:Key="Instance.Install.ToolTip.GameRunning">Cannot change the version while the game is running</sys:String>
 
     <!-- Instance.Export -->
 
diff --git a/PCL.Core/App/Localization/Languages/zh-CN.xaml b/PCL.Core/App/Localization/Languages/zh-CN.xaml
index 4834027e9..4583c6e92 100644
--- a/PCL.Core/App/Localization/Languages/zh-CN.xaml
+++ b/PCL.Core/App/Localization/Languages/zh-CN.xaml
@@ -799,6 +799,7 @@
     <sys:String x:Key="Instance.Install.NoExtraInstall">无附加安装</sys:String>
     <sys:String x:Key="Instance.Install.Reset.Message">你正在重置当前实例。&#xA;PCL CE 将会重新联网下载该实例所需的文件，并重新安装模组加载器（如有）。&#xA;此操作不会丢失你的存档、模组、资源包等。</sys:String>
     <sys:String x:Key="Instance.Install.Reset.Title">重置此实例</sys:String>
+    <sys:String x:Key="Instance.Install.ToolTip.GameRunning">无法在游戏运行期间更改版本</sys:String>
 
     <!-- Instance.Export -->
 
diff --git a/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml b/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml
index 1d658d7f2..d0505f839 100644
--- a/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml	
+++ b/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml	
@@ -400,7 +400,8 @@
                                      Click="BtnSelectStart_Click"
                                      HorizontalAlignment="Center" VerticalAlignment="Bottom" IsEnabled="False"
                                      LogoScale="0.95"
-                                     SvgIcon="lucide/download" />
+                                     SvgIcon="lucide/download"
+                                     ToolTipService.ShowOnDisabled="True" />
         </Grid>
         <local:MyCard HorizontalAlignment="Center" VerticalAlignment="Center" Margin="40,0" SnapsToDevicePixels="True"
                       x:Name="PanLoad" UseAnimation="False">
diff --git a/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml.cs b/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml.cs
index fe5e3e0b2..1545ca0f8 100644
--- a/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml.cs	
+++ b/Plain Craft Launcher 2/Pages/PageInstance/PageInstanceInstall.xaml.cs	
@@ -36,6 +36,8 @@ public PageInstanceInstall()
     private void LoaderInit()
     {
         disabledPageAnimControls.Add(BtnSelectStart);
+        // 游戏运行期间禁用"开始修改/重置"按钮（防止文件被游戏占用导致崩溃 #3494）
+        ModVideoBack.GamingStateChanged += (_, _) => ModBase.RunInUi(_RefreshStartButtonState);
         // PageLoaderInit(LoadMinecraft, PanLoad, PanBack, Nothing, DlClientListLoader, AddressOf LoadMinecraft_OnFinish)
         PageLoaderInit(LoadMinecraft, PanLoad, PanAllBack, null, ModDownload.dlClientListLoader, _ => GetCurrentInfo());
         LoadOptiFine.StateChanged += (_, _, _) => { OptiFine_Loaded(); ReloadSelected(); };
@@ -96,6 +98,18 @@ private void Init()
 
     #region 安装
 
+    /// <summary>
+    ///     根据游戏运行状态刷新"开始修改/重置"按钮的可用性。
+    ///     游戏运行期间禁止修改或重置实例（防止文件被游戏占用导致崩溃），
+    ///     并显示提示 Tooltip。
+    /// </summary>
+    private void _RefreshStartButtonState()
+    {
+        var blockedByGame = ModVideoBack.IsGaming;
+        BtnSelectStart.IsEnabled = !blockedByGame;
+        BtnSelectStart.ToolTip = blockedByGame ? Lang.Text("Instance.Install.ToolTip.GameRunning") : null;
+    }
+
     private void BtnSelectStart_Click(object sender, MouseButtonEventArgs mouseButtonEventArgs)
     {
         // Quilt 实例无法通过安装管线重装/修改（已移除 Quilt 安装支持）
@@ -442,7 +456,7 @@ private void ReloadSelected()
         // 主预览
         ItemSelect.Title = PageInstanceLeft.McInstance.Name;
         ItemSelect.Logo = GetSelectLogo();
-        BtnSelectStart.IsEnabled = true;
+        _RefreshStartButtonState();
         if ((selectedInfo ?? "") == (currentInfo ?? ""))
         {
             ItemSelect.Info = selectedInfo;
@@ -1034,7 +1048,7 @@ private object GetCurrentOptiFabric()
     public void GetCurrentInfo()
     {
         ClearSelected();
-        BtnSelectStart.IsEnabled = true;
+        _RefreshStartButtonState();
         var currentInstance = PageInstanceLeft.McInstance.Info;
         _vanillaName = currentInstance.VanillaName;
         if (currentInstance.HasLiteLoader)