Re: why can't I open my windows 10 mail and calendar
It could be possible that they are needing an update from the Store. Open the Windows Store app, click on your round person icon, then click or tap Downloads. From there, click or tap Check for Updates, and update the mail and calendar apps. Both have had updates recently and will be required to be re-installed.
If they are up-to-date, then I'm not sure what is happening, but you could try to uninstall then reinstall them from the store.