Why is MySQL hanging?

Question

MySQL

Copied records from one table to another, totaling about 18 million records.
After about 8m stopped the process (ctrl + c in muscle terminal). The process was killed, but everything hung on query aborted. I pressed ctrl + c again and successfully terminated the request.
Then I performed service mysql restart and it hung back. Then by pressing ctrl + c I rebooted the server.
Now selects from the table to which the data was copied take several minutes, although indexes are used. The site slows down, in pma 504 it throws an error when opening a database (not a table), it connects to the normal database through the console.
Here is the error log