There is still quite a bit you can do.
Windows 10? Try running the built in troubleshooters. The troubleshooters may find and fix something.
Another option is "sfc /scannow"
Reference:
https://www.lifewire.com/how-to-use-sfc-scannow-to-repair-windows-system-files-2626161
The next step would be reinstalling the GPU drivers via the manufacturer's website.
If no change then try, as best you can, to swap components.
Any other known working video cables that you can swap in? Maybe borrow from another computer or via family and friends. ( Quarantines and social distancing permitting....)
Does the computer's motherboard and CPU support integrated graphics (iGPU)? If so, try using the motherboard's video ports instead of the GTX 1070.
Use another known working monitor (or even a TV that supports computer input).
Try the current monitor on another known working computer. Determine if the problem follows the monitor or stays with your computer.
Lastly consider the VGA to HDMI adapter. Such products are often cheaply made and can fail. Do a visual inspection of the pins and ports. Look for signs of damage or debris.
Key is to identify directly or by elimination the source of the problem.