As I said, just because the TIFF *looks* black does not mean there is no data in it. Regular image viewers are often not capable of correctly displaying DEM data, especially when such data is 16 or 32 bits per channel (which it will be if you download it from the USGS).
If you provide specific information about the data you are downloading (area/location or file name), or share the actual files (e.g. with WeTransfer), then we may be able to help further.
- Oshyan