What version of JBoss AS? What OS? What JVM?
What is the CPU usage?
Try this - undeploy all of your apps, including the datasource. Bring up JBoss AS and try to access the home page and do a CTRL-C. Does it respond? If so, then good. Now repeat the same thing several times, each time adding in one more app (start with the datasource, then the EJB JAR, then the WAR). That should help identify which app is causing the issue.
I have reinstalled from zero and made some changes so it works along with other instance I need to be started. It started up again, but now when trying to access the page it throws an error right away
The installation is on Win XP
Is a JBoss 4.2.2
Java jdk 1.5
Are you doing this within Eclipse? If so, don't. Do everything from the command line.
When posting exceptions, post the full stack trace, not just the error message. Also, don't bother posting exceptions that show up in the browser - they are usually useless. There should be a corresponding exception in the console log - post that.
Also, when posting what you are doing, please be exact and specific. Phrases such as "and made some changes so it works along with other instance I need to be started" give me no clue as to what it is that you did, and "other instance" could mean anything. Instance of what???