If you still have your original license, you can download the final stable installer from the Official Steinberg Support Page .
Steinberg officially ended support for Cubase 5 years ago. It was built for Windows XP and Windows Vista/7 (32-bit). Windows 10 operates on a fundamentally different architecture, including driver model changes (WDM/ASIO updates) and the phasing out of legacy 32-bit-only applications in some configurations.
The security risks far outweigh any nostalgia or perceived convenience. If you own a legitimate license, attempt to recover the installer through official Steinberg channels. Otherwise, invest in a modern DAW – even the entry-level Cubase Elements will run better, support your audio hardware, and receive updates.