Mac applications refuse to launch
You can fire up the /Applications/Utilities/Console.app and look over the logs as you are launching programs.

If the messages are not clear, you could either edit some details in the question or post a new question for each app / message that has you stumped as to a cause or solution.

Of course, you also might try some generic troubleshooting steps like rebooting, checking the apps with a new user, etc...