I have finally found the answer to this Vostro Windows 7 Freeze every morning. The issue began happening on a OptiPlex 380 also.  When the video driver gets updated through Windows update, it causes the DVI card purchased from Dell, to have issues. The fix is to install the old, original driver. I found a Toshiba program that contains the driver. google   driver_video_intel_TC00171500F. As for as I can tell, Dell does not have this driver available and is no longer selling this DVI card with their systems.  
I have 2 Dell Vostros, one is a 32 bit  Windows professional, the other is a 64 bit Windows Professional. The 64 bit began locking up at night while PC was idle. I first suspected the Trend Micro Virus Scanner. After reloading the good image (One that does not lock up) I have traced it to being  a certain window update that is causing the lockup issue.  I am not sure which Windows update it is... I have been running the 64 bit for 4 month with no lockups, but it has the original Dell Factory Windows load (no updates). This week it was brought to my attention (this week)  that the other Win7 Vostro (32 bit) is no doing the exact same thing.  The lockups occur at night, and user must reboot in order for the PC to work again. Sleep is turned off,  Sometimes you can move the mouse, but have a blank screen. Sometimes the cursor just sets and spins. The 64 bit PC with the same issues did the same thing before I reimaged and turned windows updates off.  Auto hide taskbar is turned off. We have several Dimension 380's running windows 7 (32bit) that we have never had an issue with. I would suggest to any considering buying a vostros, DON'T. It has been over 8 months with nothing but headaches due to Windows 7 and these VOSTRO PC's . Today I will reload the 32bit pc image and turn off windows updates. I am a DBA/DB programmer having to diagnose these issues when able. I am certain that it is a windows updates causing the issue with the vostros, and I do not have the time to troubleshoot a Dell & Microsoft issue, and apparently their experts are unable.  
2 DELL Vostro Freezing and locking up Win7 Windows 7 lockup 32 bit & 64 bit