alfresco, tomcat crashes on startup, no clues in the logs

I have installed an alfresco community edition 4.0 on a Win 2003 R2 with 3GB of RAM.
I've used alfresco for some hours, i've created a user, uploaded some documents. But now, restarting it, tomcat crashes during startup.

The logs are VERY poor: these are the last lines of conf/jakarta_service_20120420.log

[2012-04-20 15:45:07] [info] Commons Daemon procrun (1.0.2.0) started
[2012-04-20 15:45:07] [info] Running Service...
[2012-04-20 15:45:07] [info] Starting service...
[2012-04-20 15:45:08] [info] Service started in 1296 ms.

The last lines of conf/stderr_20120420.log

20-apr-2012 15.45.09 org.apache.catalina.core.StandardService start
INFO: Starting service Catalina
20-apr-2012 15.45.09 org.apache.catalina.core.StandardEngine start
INFO: Starting Servlet Engine: Apache Tomcat/6.0.29
20-apr-2012 15.45.09 org.apache.catalina.startup.HostConfig deployDescriptor
INFO: Deploying configuration descriptor alfresco.xml
20-apr-2012 15.45.10 org.apache.catalina.core.StandardContext addApplicationListener
INFO: The listener "org.apache.myfaces.webapp.StartupServletContextListener" is already configured for this context. The duplicate definition has been ignored.
20-apr-2012 15.45.12 org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring root WebApplicationContext

The conf/stdout_20120420.log is empty.

I need to improve the troubleshooting process so:

1) how to increase the log level?

I replaced "FINE" the with "ALL" in conf/logging.properties, but nothing changed.

2) any other suggestion on troubleshooting startup is appreciated :-)