Many of us have been having this problem, since BIOS V2.4.0 was released. All BIOS since then have caused the problem, each release is slightly better as it seems to be longer between lockups. All have in common, one of the BIOS versions and an Nvidia card. Only recovery, power off and then back on with the power button. No eminent sign of failure (error display, dialog boxes, etc.) or Events logged to the Event Viewer other then Error 41 is due to shutting down Windows improperly. Search the Forum here for 8940 freeze or lockup, you'll find many subjects. Only work-around so far, go back to BIOS V2.3.0.
For the past couple of weeks I have been having my desktop/windows freeze/lock up randomly.  Its happened a few times.  I thought it was happening because I started putting my computer to sleep/hibernating manually when leaving.  However since I stopped doing that it as occurred a few more times after that.  This was happening prior to and after updating my bios to 2.8.  Also is happening prior to and after updating my Nvidia graphics driver 516.59.  Does anyone know the reason why this may be happening?
XPS 8940, last couple weeks, freezing