Check for other processes on port 8001: sudo netstat -nlp | grep 800 is a good start. If there is anything else on port 8001 you will have to shut it down, at least while configuring MarkLogic for the first time. After that you might be able to shift the admin server to a different port, but that's not trivial.
Once port 8001 looks clean, check to make sure MarkLogic is running. Try sudo service MarkLogic restart and see if there are any console messages. Then check /var/opt/MarkLogic/Logs/ErrorLog.txt for startup messages.
You might also try these instructions for resetting the local data directory and starting over. In your case the data directory should be /var/opt/MarkLogic.
Thank you so much for your help. The problem is solved now. I was trying sudo netstat -nlp | grep 800 command when MarkLogic service was running, so it was showing me that port 8001 is in use by MarkLogic service and 8002 by java. When I stopped MarkLogic service, and then checked for port 8001 - it was in use by java. So I killed the java process and again started MarkLogic service. It worked for me. Thanks a lot.
ps -ef | grep MarkLogic) The forbidden access on port 8000 is likely because you haven't yet gone through the setup process on port 8001, and should clear up once you've set up the admin user. - Dave Cassel