The sandbox version is 5.4; I am a newbie:)
I drag the assets to the Assets folder, but any assets(except the 5.4 GameSDK) can't be loaded normally,
The models can be loaded, but the texture is the replace me texture
When replacing the texture using the corresponding assets, the sandbox crashes with no reports
Help me please:)

Can you give some details on your material setup (screenshot), what and where the models come from (Max/Maya/Blender)?
Have you submitted a crash report if the edit has crashed?