Please double check, if db.xml properly configured or not. Make sure connection details which you configured is uncommented and others section in the db.xml properly commented.
As per my knowledge after db.xml configuration, your MWS should come up once you start the MWS…
Hope you installed the tables for MWS.
and double check the log file in the MWS\server\default\logs\
#MWS-CAF-Task-Engine#webMethods-BPMS#webMethods