error: mysql shutdown unexpectedly.

                                    1_ Rename the folder mysql/data to mysql/data_old (you can use any name)
2_ Create a new folder mysql/data
3_ Copy the content that resides in mysql/backup to the new mysql/data folder
4_ Copy all your database folders that are in mysql/data_old to mysql/data (skipping the mysql, performance_schema, and phpmyadmin folders from data_old)
5_ Finally copy the ibdata1 file from mysql/data_old and replace it inside mysql/data folder
=> Start MySQL from XAMPP control panel
*************************DONT DELETE ibdata1 FILE*************************

                                    Stop there! Please do not delete anything!

Some of the answers in Stackoverflow or in other platform could leave completely unusable your database!, so, before deleting files, first try to do what the error message in XAMPP message panel recommend you to do, using the MySQL backup folder which is included with XAMPP. So do the next:

Step 1. Rename the folder c:\xampp\mysql\data to c:\xampp\mysql\data_old (you can use any name).

Step 2. Create a new folder c:\xampp\mysql/data.

Step 3. Copy the content that resides in mysql\backup to the new mysql\data folder.

Step 4. Copy all your database folders that are in mysql\data_old to mysql\data (skipping the mysql, performance_schema, and phpmyadmin folders from data_old).

Step 5. Finally copy the ibdata1 file from mysql\data_old and replace it inside mysql\data folder.

Step 6. Start MySQL from XAMPP control panel.

And, Its DONE . No databases lost, no ports changed, no run as administrator, no force recovery, no kill mysqld process, no restoring from previous versions, no more errors.

                                    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.

                                    Instead, first try using the MySQL backup folder which is included with XAMPP. So do the next:

1.Rename the folder mysql/data to mysql/data_old (you can use any name)
2.Create a new folder mysql/data
3.Copy the content that resides in mysql/backup to the new mysql/data folder
4.Copy all your database folders that are in mysql/data_old to mysql/data (skipping the mysql, performance_schema, and phpmyadmin folders from data_old)
5.Finally copy the ibdata1 file from mysql/data_old and replace it inside mysql/data folder
6.Start MySQL from XAMPP control panel
And, voilà!

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