Open the Console – the last few lines almost always reveal the reason.
- Not enough memory (“OutOfMemory”, crash after loading mods): use fewer mods or upgrade your plan.
- Broken or incompatible mod: remove the most recently added mod and restart.
- Missing token/licence: some games need their own key (see the article for your game).
- Error after an update: restore a backup from before the update.
If that doesn't help, send us a ticket with the last few lines from the Console. You can also check the status page to see whether there's a known outage right now.