I recently upgraded my Dell Studio 1558 laptop from the orignal Windows 7 Home Premium 64-bit OS to the Windows 7 Ultimate 64-bit OS. Now, whenever I try to shut down my laptop, it displays the normal "Shutting Down" screen. However, it stays on the screen indefinitely, and my laptop never shuts down. Then, I have to manually press the power button to turn it off. However, there are no error messages at all. I do not even get the message saying Windows had shut down improperly last time. Please help me. Thanks.