At the beginning of your post you stated that you performed a windows update, and the issue started afterwards. Then near the end you said no major changes in hardware/software.
Personally, i would concider and issue starting right after a windows update somewhat linked to the software changes (even if you dont concider them major, you still admitted to the update right before it started which tells me you acknowledge the suspect timing)
Anyway, that said, it could be useful to provice a little more information on the particular updates that you processed at that time. You could also try rolling back / uninstalling those particular updates, if the issue stops after the rollbark/uninstall then you can try adding them back one at a time to see if there is any specific update that is causing the issue.
Alternatively it could not be related to the updates at all, judging from your post i am assuming you never rebooted after moving mirc to d:, not until performing updates that may have required the reboot. It is possible that something in windows that is causing the issue was no activated until after the reboot. But it certainly doesnt hurt to rule out the updates as a direct or indirect cause.
