mdb that can work in Access 2013 doesn't work in Access 2021

[manabn]

My parent old work PC finally broke down, so I bought a new PC (Windows 10 Home 64bit) and Microsoft Access 2021 (download version, perpetual license) to take over the Access 2013 ledger files (mdb format) that were running on the old PC.
However, the mdb files don't work properly in Access 2021.

When mdb is opened, a yellow band at the top reads "Security Warning Some active content has been disabled. Click for more information." and to the right of that, the button "Activate Content" will appear.
When I enable it to work, "Cannot run Microsoft Access program." dialog box appears and the entire Access program is terminated.

I know from web searches that mdb is older format and have tried to convert to accdb, but can't get it to work.

I consulted Microsoft Support, but they replied that downgrading from Access 2021 to 2013 isn't possible due to different licensing reasons, and recommended this support.

What should I do to take over my parent's ledgers mdb?

[#2]

Are you able to post the database here for someone to look at it

[#3]

@manabn 

For starters, I think that message indicates that the mdb is not in a Trusted Location on this new computer. 

If designating the folder where it is located doesn't restore proper functionality, post back and we'll follow up further.

[#4]

you can create a New .accdb database and import All Objects from your Old .mdb database.