I had a similar issue with windows 10 back few days. Try to check if removing the file called "d3d9.dll" allow you to have access to the game.
What ENB did you install?
Seriously... get another ENB.
CryENB uses Adaption which IV:MP doesn`t support, so it is not a surprise that you crash and if you can somehow play the ENB on IV:MP succesfully it will give you brightness, contrast and texture issues.
Try moving your GTA IV game folder somewhere else out of Program files, then enable "Override high dpi scaling" in the LaunchIVMP application.
Get 10
10 is worse than 8.1 unless you want to benefit from DirectX 12 and a lot of annoying updates.Benefit from DirectX 12? The only way anyone is going to really profit from it at its full potential is by playing a game that is built from the ground up using that API. Otherwise, it wouldn't really work too well, even though it does get more draw calls compared to its predecessor, DirectX 11.
Benefit from DirectX 12? The only way anyone is going to really profit from it at its full potential is by playing a game that is built from the ground up using that API. Otherwise, it wouldn't really work too well, even though it does get more draw calls compared to its predecessor, DirectX 11.