You receive a error message in Kaseya relating to "Unable to access database" _and_ upon checking the database status in SQL Management Studio, you see that one or more databases shows "Suspect" next to their name.
This is not a Kaseya problem per se. Kaseya requires the SQL database server and the database that it uses to be operational.
When SQL finds a problem with a database, it marks it as suspect, meaning that there may be a problem. In order to prevent further data loss, SQL will not allow the database to start, and will instead flag it as "suspect".
Until the database is checked for errors and confirmed as good, the database will not be able to start, and therefore Kaseya will also fail to start.
There is a great step-by-step article below that walks you through the steps to return the database to a working state, or at least to identify the reason for the failure and take steps to recover.
If for any reason the database cannot be recovered, the only option is the restore from backup.