The Laptop Dell Precision 7520 running under Windows 7 with default settings has severe stability problems. Even with the newest BIOS and driver updates the system freezes (i.e. showing a black screen) when waking up from suspend-to-RAM.
The system stability can be improved (freezes still might happen from time to time) by disabling the switchable graphics in BIOS:
The switchable grapics setting allow the OS to switch dynamically between the builtin Intel graphics and the faster but more power consuming NVidia graphics card. Apparently the drivers and/or hardware can’t handle this switching correctly.