Hi,
When you say it's not being detected, did you check Device Manager and under Display Adapter it's not showing up correct?
- First do a clean install of the graphics card.
- Uninstall anything related to Nvidia from Device Manager and Programs and Features.
- Once uninstalled, go to Nvidia's website and see if it will be detected and have a driver for it.
- Here's the link:
http/www.nvidia.com/Download/index.aspx
- If it will be detected proceed with installing it's driver.
- If all these will not work, I would suggest opening the laptop again and make sure that everything is seated properly specially the GPU.
Here's a video guide on how to disassemble your laptop.
https/www.youtube.com/results?search_query=alienware+17+disassembly