OK, a few other things to try:
1. If you haven't done it yet, try reading CapnScurvy's write-up on LAA
Windows10; Large Address Aware; SH4 Install. It's about Windows 10 and LAA, but applies for any 64-bit Windows with 4Gig or more of RAM.
2. Go to your game folder, and right-click on SH4.EXE, and choose "Properties" from the context menu that comes up. Click on the "Compatibility" tab. Tick the box for "Disable display scaling on high DPI settings". You could also try the "Run this program as an administrator".
3. Last (for now) and certainly not least, where did you get your game from, and is it download or disk? What disk / folder did you install the game to?