Not using Win10, so can't advise specifically for that version.

Does this still happen after you re-boot windows? In the 'processes' tab of task manager, does it show mirc.exe as using a high percent of the CPU?

This is a trouble-shooting info that has often been asked of people having problems like this, can you paste this line into any mirc window, and reply here with the text that results:

Code:
//echo -a $os $version $beta $md5($mircexe,2) $file($mircexe).sig $alias(0) $script(0) $dll(0) $com(0)