Unreal Engine 4 crashed

Hi! I was learning to make games, the i started editing landscape in my game scene, then i saved my work and closed UE4. But next day when I launched UE4 it showed me an error [Unreal Engine is exiting due to D3D device being lost. (Error: 0x887A0020 - 'INTERNAL_ERROR)]. I am posting image of that error. Please help me solving it. Please reply.