ubuntu 11.04 crashes while booting on HP probook 4530s

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http://askubuntu.com – I am new to ubuntu environment I had installed 10.10 yesterday and then upgraded it to 11.04 then I installed java according instruction provided in 2nd answer of following thread How do I install Oracle JDK 6? It worked perfectly well but after restarting my computer it hangs on the boot,there are some threads with a similar problems but that does not seems helpful to me like Ubuntu hangs on booting up after a update can someone help me out with this problem considering that I dont have enough knowledge of operation system and environment Regards Ahsan (HowTos)