Case #1:
"RMMZ now requires WebGL compliant graphics cards. Without WebGL you're not going to playtest anything.
Currently about 90% of the PCs in use worldwide support WebGL though, so your playerbase should not be too affected."
That's what I found in the forums about this issue. Are you able to run any MZ game?
It's not because your computer isn't powerful enough, it just seems to be not compatible with WebGL ( required for RPG Maker MZ ).
OR Case #2:
It seems windows 8 isn't compatible with RPG Maker MZ.