Answer

Check The Post Status For The Entry

Make sure that your entries are set to a status of Published and not Unpublished¹. If you change the setting, you must remember to save the entry to update your site.

Check Your Default Weblog Display Settings

By default, Movable Type will use the Entries to Display setting in Settings > General : Default Weblog Display Settings² to determine how many entries to display on the page (as well as on your other index templates).

If you've chosen days for the setting, you may not have any recent entries that fall within the number of days you have specified. (Note that, if you choose 7 days, 7 days means the last 7 consecutive days, not necessarily the last 7 days on which you posted an entry. So if you have posted on just 3 of the last 7 days, only the posts from those 3 days will be listed on your main indexes.)

Change Or Override The Default

In version 3.2 or higher, to ensure there will always be entries displayed on your main index page even after a rebuild, choose entries for the Entries to Display setting instead.

In any version, you can also use the lastn attribute on the <MTEntries> tag in your template:

<MTEntries lastn="10">

That will always display the ten most recent entries published to your weblog.

¹ In versions prior to 3.2, make sure that your entries are set to a status of PUBLISH and not DRAFT.

² In versions prior to 3.2, this is the Number of Days Displayed setting in Weblog Configuration > Preferences.