Bad magic number in disk label.

This is first time post...found this forum when looking for possible solution to fix my sun pc. Just one day can't boot it already showing the following:

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Boot device: disk File args:
Bad magic number in disk label
Can't open disk label package
Evaluating: boot

Can't open boot device

ok
ok
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Am losing hope already, want to fix this hard disk and retrieve important files. Really appreciate anyone can help me....thanks a lot.