2
Check with your host provider if they made any changes to the configuration, e.g. MySQL or PHP versions updates.
Also, try to change a theme in the Admin to "Default" or "Zetagenesis" and see if this makes a difference.
Normally, XOOPS cannot have blank start page out of nothing, i.e. there had to be some changes to the environment.
Also, you might try with a different browser, just in case...