On the windows 7 32-bit machine, install the latest Blackmagic driver, and Nuendo not seeing the Blackmagic card. The device list empty (only Onscreen window active).
Outside the Nuendo, the Blackmagic Card works properly with Black Magic Media express.
I had this problem and I can’t quite remember how I fixed it.
I think I un installed ( reboot) and reinstalled the blackmagic drivers, to get it back.
Also try powering the computer off at the mains for 10 seconds then restart, if the driver thing does not work.
Before install/update blackmagic driver, it is necessary to delete the Win7/Program Files/Quicktime/QTComponents/BlackmagicCodec.qtx file. When uninstall/reinstall/upgrade Blackmagic driver, the installer application do not delete the old BlackmagicCodec.qtx file. It’s that simple.