The sound on my Dell Latitude E6510 isn't working?

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http://askubuntu.com – It was working fine yesterday on both Windows and Ubuntu 12.04. It usually does this every few days and I just have to re-start the laptop but I've done it Three times and it's still not working... I googled it but nothing relative to my problem came up... Can any body tell me what is wrong with my laptop? Is it hardware matter issue or a software one? Thanks in advance (HowTos)