When a server does not return for a full hour or more following a restart, most of the time the reason is your mods. Some mods are incompatible with newer versions of the ark server software. Some mods are incompatible with other mods.
If you removed all mods and the server still won't come up, there are cases where your save files become corrupt. You can always make a backup of your save files through the Backup tab, then wipe the server to remove them. The wipe option is the "-" on the Servers page. If that fixes it, then your save files were corrupt and you'll have to start fresh without them.
Unfortunately, the ark server software doesn't give any hints about what is causing the problem. That means you'll need to use trial-and-error to find the culprit.