Index: /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.cpp	(revision 27405)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.cpp	(revision 27406)
@@ -155,4 +155,6 @@
         mTwDisplay->setTabEnabled (1, false);
     }
+
+    checkMultiMonitorReqs();
 }
 
@@ -286,4 +288,5 @@
 {
     mLeMonitors->setText (QString().setNum (aVal));
+    checkMultiMonitorReqs();
 }
 
@@ -292,2 +295,19 @@
     mSlMonitors->setValue (aText.toInt());
 }
+
+void VBoxVMSettingsDisplay::checkMultiMonitorReqs()
+{
+    int cVal = mSlMonitors->value();
+    if (cVal > 1)
+    {
+#ifdef VBOX_WITH_VIDEOHWACCEL
+        mCb2DVideo->setChecked(false);
+#endif /* VBOX_WITH_VIDEOHWACCEL */
+        mCb3D->setChecked(false);
+    }
+#ifdef VBOX_WITH_VIDEOHWACCEL
+    mCb2DVideo->setEnabled(cVal == 1 && VBoxGlobal::isAcceleration2DVideoAvailable());
+#endif /* VBOX_WITH_VIDEOHWACCEL */
+    mCb3D->setEnabled(cVal == 1 && vboxGlobal().virtualBox().GetHost().GetAcceleration3DAvailable());
+}
+
Index: /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.h
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.h	(revision 27405)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.h	(revision 27406)
@@ -62,4 +62,6 @@
 private:
 
+    void checkMultiMonitorReqs();
+
     CMachine mMachine;
     QIWidgetValidator *mValidator;
Index: /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.ui
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.ui	(revision 27405)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/settings/vm/VBoxVMSettingsDisplay.ui	(revision 27406)
@@ -172,5 +172,5 @@
              <widget class="QIAdvancedSlider" name="mSlMonitors">
               <property name="whatsThis">
-               <string>Controls the amount of virtual monitors provided to the virtual machine.</string>
+               <string>Controls the amount of virtual monitors provided to the virtual machine. Currently 2D and 3D acceleration isn't available when more then one monitor is selected.</string>
               </property>
               <property name="orientation">