Q: What should I do if the MC printer suddenly won't open?
Q: How to restart the MC printer?
A: Please follow the below steps:
Step 1: Open Task Manager
Press Ctrl + Alt + Del on your keyboard (CANC on some keyboards), then select “Task Manager” from the pop-up menu

You can also right-click the toolbar and select Task Manager to open it.

Step 2: Terminate all the Java™ Platform SE binary task
In Task Manager, locate Java(TM) Platform SE binary (❶).→ Click on the process and select "End Task" in the bottom right corner (❷).
As shown in the picture:

Alternatively: Click on the process and select "End Task" in the upper right corner (❷).

Step 3: Restart the MC printer.
Locate MC PRINT on your desktop → Double-click to open the MC Print client → Enter the password as 123456 → Click Login

Kind tips:
If the problem persists, it is recommended to check if there are any other related processes that need to be terminated, or to restart your computer and try again.