Technical FAQ

My UnrealEd is white
UnrealEd shut down your viewports for some reason. Click View -> Viewports -> Configure -> Ok to restore them.

I die when I test my level
Click Build -> Rebuild Geometry Only before you test your level. If you can Rebuild All instead. Anything as long as the Geometry is rebuilt.

I can't select things
Antialiasing is enabled in your display driver's options. UnrealEd doesn't work as long as it's on. Set it to Off or Application Controlled.
If this does not solve your problem (though it most likely will!!!) you may have accidentally disabled the Selection Highlight so you are selecting things just fine, they just don't light up blue/green. Click to gray bar at the top of your viewport and select View and make sure Show Selection Highlight is checked.

My textures are replaced with the green bubbly default texture when I test my level
The most common cause for this is that you imported them into a package other than myLevel and forgot to save it before you tested your map. Separate packages are not saved automatically.

My StaticMeshes don't show up when I test my level
See "My textures are replaced with..." and mentally replace Textures with StaticMeshes.

My map/ Parts of my map disappear when I add/subtract a brush
You have a BSP-hole in your map. Read this!