Possible Solution #1:
From the NVIDIA Control Panel:
1. Select 3D Settings-> Manage 3D settings
2. Select The Tab "Preferred graphics processor
3. Select High performance Nvidia processor.
Possible Solution #2: Make sure your video card drivers are up to date.
Is it possible that your computer doesn't meet the minimum requirements. The minimum requirements for DD2 are:
OS: Windows XP
Dedicated Video Card memory: 256mb or more
Processor: 2.0 Ghz Dual-Core CPU
Memory: 2 GB RAM
Graphics: ATI Radeon HD 2600 or better / NVIDIA GeForce 8600 or better, 512 MB video memory, with Shader Model 3 support
DirectX: Version 9.0
Network: Broadband Internet connection
Hard Drive: 4 GB available space
Sound Card: DirectSound-compatible sound device
Additional Notes: Internet connection is required to play.
If none of these solutions solve the issue, click here to submit a bug report.
Keep in mind that our support team works Monday through Friday, 8 a.m. to 5 p.m. EST.