Check out example codes for "Error: MySQL shutdown unexpectedly.". It will help you in understanding the concepts better.

Code Example 1

1. Exit Xampp and navigate to xampp/mysql/data directory
2. delete the ibdata1 file
3. restart the XAMPP server

or

1. Exit Xampp and navigate to xampp/mysql/data directory
2. delete the ibdata1, ib_logfile0,ib_logfile1,ib_logfile101 files
3. restart the XAMPP server

or

Try to check the error log at the installed location: /xampp/mysql/data/mysql_error.log

Code Example 2

go to Xampp and navigate to xampp/mysql/data directory
delete all files and dir
and paste files in backup directory

Code Example 3

1. Exit Xampp and navigate to xampp/mysql/data directory
2. delete the ibdata1 file
3. restart the XAMPP server

or

1. Exit Xampp and navigate to xampp/mysql/data directory
2. delete the ibdata1, ib_logfile0,ib_logfile1,ib_logfile101 files
3. restart the XAMPP server

or

Try to check the error log at the installed location: /xampp/mysql/data/mysql_error.log
This can help you better debug the problem.
Also Note:

1. XAMPP might hit into port issue when you have skype also running.
2. There is a federated plugin issue that is common.

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