As iimki says, there is a setting in "Options > Video > Advanced" called "Stop after a long pause". If that is checked, MC will stop playback after being paused for 10 minutes.
But that should save a Bookmark for where you are up to, and when you start playback again it should start at the correct point. Read the "Bookmarking" Wiki article to see if you can work out why that isn't happening.
The Windows 8.1 error is a strange one. Maybe make sure you have backups of the MC Library, uninstall both MC23 and MC24, then do all Windows updates, and reinstall MC24, restore the backup, and try again. Some Windows updates have been breaking stuff, and a clean reinstall seems to help sometimes.