Since Windows 8 is an older OS, you must ensure you are downloading a "legacy" version. Vegas Pro System Requirements | PC Specs & GPU Support
VEGAS Pro 16 is the last official release to include full support for Windows 7, 8, and 8.1. sony vegas pro download for pc windows 8
If you are running a 32-bit version of Windows 8, Vegas Pro 11 is the final version that supports 32-bit systems. Versions 12 and later require a 64-bit OS. Since Windows 8 is an older OS, you