It could happen that the GPU process crashed and it is still hanging, even after you close the program down. After all we are dealing with thousands of parallel operations. The best advice would be - restart the computer - it should clean all hanging processes and pipes.
Why it needs modern graphic card?
The actual calculations are done by your GPU (graphical card) not CPU (processor) because of the parallelism needed for fast calculations - GPU have much more cores that can run calculations all at the same time. Your processor has probably 4 to 8 cores, but even lower end GPU’s have 700-1000 cores and the newest gaming video cards like RTX-3080 Ti have now 10,000 cores. That is an enormous difference and it is truly like having a supercomputer at your disposal. Running the calculations on the CPU alone would not be realistic.
The output is black or just noise
It means the vulcan library can’t correctly work with your GPU driver. Try to update your video card drivers:NVIDIA: GeForce ExperienceAMD: you need to install AMD Adrenalin version (at present Adrenalin 22.6.1) as it includes their own Vulcan driver.If nothing helped, try using CPU mode (it will work, but it will be very slow)
CPU Only mode is a fallback when nothing else works. It will use only your CPU cores - so instead of 1000s of GPU cores, you will be running it with only a few CPU cores. It will be about 10-20x slower than with GPU to the point that you may not even bother. Sorry, but that’s how it is these days.
AMD Graphic cards
For recent AMD cards you have to install AMD Adrenalin version (at present Adrenalin 22.6.1) as it includes their own Vulcan driver, otherwise the output would be black.
Vulcan seems to like NVIDIA and even a mid-tier models such as GTX 1650 or GTX 1660 usually work well. Always make sure you get the newest NVIDIA drivers using GeForce Experience. (They update drivers very often)
Use menu Tools - Test GPU then press Run Benchmark Test button. The result of the test should be similar to this. Make sure the image on the right after the test is complete (not blank, no noise)