Windows 8.1 is a preview and is not complete. It is still in development. It is essentially a public release candidate, while they collect data from it and continue to develop internal builds until no errors are found. Your NVIDIA card is also DirectX 10 and should be fine for this OS. If it runs Windows 7, it will generally run Windows 8. It does not require UEFI. You just buy Windows 8 and see if that works. The difference between 8 and 8.1 is not extremely different. There is no way to say "this pre-release software is not working" and feel justified that no one has answered. It is an incomplete pre-release. I have no intent to offend you, but this is reality.
If you can provide the exact error code, maybe this can be diagnosed, by searching for existing Windows 8 error codes.
If its a Blue Screen stop code, the exact 0x number is needed a long with the error message you are getting. More information is needed to diagnose your problem.
Also, please provide full system specifications, including motherboard, chipset, CPU, memory, HD space, video graphics, network adapter, etc.
Windows 8.1 Preview and Windows RT 8.1 Preview are stable and have been thoroughly tested, but aren't the finished product. Your PC could crash and you could lose important files. You should back up your data and you shouldn't test the preview on your primary home or business PC. You might also encounter problems like:
- Software that doesn’t install or work correctly, including antivirus or security programs.
- Printers, video cards, or other hardware that doesn’t work.
- Difficulty accessing corporate or home networks.
- Damage to some of your files.