Microsoft provides to its users a very detailed installation/configuration/troubleshooting page where you can see how to install/user/troubleshoot problems related to SQL Server and all its versions. You can access it using the link posted below.
According to users on the Microsoft Tech forums, SQL 2008 Express is not compatible with any of the versions of Windows 10 that have been released. It means that Sage Pastel Debtors Manager needs to update their software in case it's still supported.
Contact the developers to ask for additional info:
Support page: https://support.microsoft.com/en-us/kb/2681562