Level editor crashes the computer

[Your Computer]

Is there any other reason?
Could it be caused by the error code 51? I have tried to verify integrity of game files. Still gives me the same error.
I tried to reinstall Steam, but I can't connect to my Steam account right now to try it.

Error codes reported by Steam are normally not related to the game itself. If the game wasn't installed properly or corrupted, i doubt it would cause a blue screen to occur. The issue described in your first post sounds like either an issue with the hardware (e.g. when my first graphics card died i would experience artifacts and blue screens before its death) or the driver (i.e. most blue screens are driver related). I'm guessing at the point that the system reported that the graphics card crashed, so did the level editor. In which case, if the system blue screens minutes after, then it implies an issue with the hardware or maybe even a setting in the BIOS.