Greetings from Monster Fenrick!
I have reproduced the guide from LegendCup[legendcup.com] (which I have originally written) into the Steam Forums, hopefully for more visibility for finding the issues as reported on the Steam version of the game.

This guide attempts to address reported issues collected from multiple sources (Steam Forums, Reddit, MR Discord etc.) with confirmed fixes.
Most issues have some solution, though there are a few rare cases that have none.

Several potential resolutions for the game not loading. Be sure to exit the game and launcher completely between each step:

1. OS is pending updates and/or hasn't been rebooted for a while

• Please, First, check if you have any pending OS updates, Apply them and allow your PC to fully reboot. Sometimes it's that simple.

2. Check for CPU instruction.

• The game absolutely will not run if your processor doesn't support SSE4.1 instructions.
  
• To check, you can download CPUID from cpuid.com.
  
• On the default "CPU" Tab look for a box labelled "Instructions" and if SSE4.1 is included.
  
• If SSE4.1 is NOT included, your hardware cannot launch the game. SSE4.1 has been included in nearly every processor roughly after 2006, so this is highly unlikely unless your PC is quite old.

3. Resolution settings issue

• Before launching the game, open up the Options tab at the game selection screen, then open the Keyboard/Resolution settings.
  Note that the small window that opens might open behind another window
  
• Try changing the resolution. If it is set to Full Screen, uncheck this option and choose a small windowed option, or vice-versa.
  
• Try to launch the game again. If the game launches, you can try setting the resultion back to your preferred setting or full screen again. Sometimes resetting this resolves the resolution conflict.

4. Setting.ini file missing/broken with Non-English Operating System

• On occasion, especially when some Operating Systems are in a different language, the Setting.ini file causes issues with loading the game, or is missing completely.
  
• Open the Setting.ini file located in C:\Users\x\Documents\KoeiTecmo\mfdx_en
  
• Replace the contents with the following text
  
  [Graphics] ScreenWidth=1366 ScreenHeight=768 [Window] FullScreen=0 [Input] UP=UP_ARROW DOWN=DOWN_ARROW RIGHT=RIGHT_ARROW LEFT=LEFT_ARROW CIRCLE=L CROSS=K SQUARE=J TRIANGLE=I L1=Q L2=U L3=F R1=E R2=O R3=H START=ENTER SELECT=N
• If your Setting.ini file is missing completely, and you are unable to create a new one from scratch, You can download the Setting.ini file from LegendCup. Unzip/Extract the file to your Documents\KoeiTecmo\mfdx_en folder to restore a working Setting.ini file. Attempt to Launch the game. If it is successful, you can exit the game and change the settings back to your preferred settings.

The January [F] (Free for All) New Year Cup is known to freeze randomly, either at load or mid-tournament. No common factor has been found to determine the cause, It could be an issue with a specific monster's texture trying to load in this tournament or something completely different; there are too many differing hardwares, configurations, etc. to pinpoint any singular root case, though it does not seem to happen on the Switch version of the game. Sadly, if you encounter this issue there is no known workaround as of yet.

For other areas of random game freezing...
Try any of the following:

1. Toggle "FF" (Fast Forward) to the opposite of what you had it on.
   
   
2. Change the resolution. (If Full screen, go windowed or vice versa).
   
   
3. If it still freezes, Update video drivers, then try the above again.
   
   
4. Some controllers, such as Fight Stick, are also known to crash the game before reaching the Launcher.

There are several reasons this could be occurring. Usually this is permissions/access related. Please try these in order from top to bottom, as the top-most option will be the simplest.

• If you have any Anti-Virus software running, try temporarily disabling it, then see if you can save.
  
• If disabling Anti-Virus works, then Steam or the Game itself (mf.exe or mf2.exe) may have been added to the Anti-Virus' block list. Find the settings for your specific brand of AV to unblock the app, then start your AV back up as usual.
  
• For example: Windows "Controlled Folder Access" options is a potential culprit that may need your application to be white-listed.

• Try launching the game's .exe file as Administrator.
  
• Navigate to the install directory SteamLibrary\steamapps\common\mfdx\[MF or MF2]\, Right Click on the MF.exe or MF2.exe and "Run as Administrator"

Double check your User account's permission isn't being denied access.

1. Exit Steam completely, and Navigate to c:\Users\[YourLogin]\Documents
   
2. Right Click on the KoeiTecmo folder, and choose Properties
   
3. Click on the Security tab
   
4. Click on your Login/User name (NOT System, and NOT Administrators)
   
5. Check that Everything is Allowed and nothing is Denied.
   
   If you see Anything Denied...
   
6. Click the Edit button to open the permissions for your Login/User.
   
7. Click on your Login/User name (NOT System, and NOT Administrators) in the Permissions window
   
8. Uncheck any boxes in the Deny column
   
9. Click Apply
   
10. Click Save

Now try re-launching Steam and the game and see if you can save.

If something happens, like a power fluctuation or outage while the is writing to the save data, there is a potential that the save data can become corrupted and will not load. On a PC connected to a UPS, or on a laptop that has a continuous power supply this is very unlikely to happen (unless the laptop battery dies during a file write... which has been reported).

Sadly once this happens, those save files are completely unusable.

However...

PREVENTION is the best medicine.
If you save your save file folder in another location, you can (at any time) copy the good files back into your save file directory and play from the point on the backup.

There are several ways to back up your save files:

• Full Manual (this is literally Copying the folder and pasting the contents of your "C:\Users\x\Documents\KoeiTecmo\" folder, which contains the saves for both games, somewhere else for later retrieval).
  
• Semi-Automated (Community tools have a button you can click that will do the copying for you, and add a date/time stamp to it automatically)
  
• Fully Automated Backups (Using PowerShell + Task Scheduler for Windows, or using Bash script in Linux) that only run if the game is being played, and will back up your KoeiTecmo folder, with time-stamps, automatically to any directory of your choosing at any time interval you desire (every 5m, 20m, 1hr, etc.)

For complete information on all 3 methods and how to set up backups and how to recover a corruption from backups: https://legendcup.com/automatic-backups-monster-rancher-dx.php