Help me pls from repeat random freeze

I have got my computer bought in Aug, everthing is fine until recently, it has random hang which force restart is needed. In some case, i can have hang in welcome screen
My setting:
i7CPU 870
ASUSTek P7H55-M
8.Gb ram
Nvidia Geforce GTX 460

I got the minidump files as follows:
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Executable search path is:
Unable to load image \SystemRoot\system32\ntoskrnl.exe, Win32 error 0n2
*** WARNING: Unable to verify timestamp for ntoskrnl.exe
*** ERROR: Module load completed but symbols could not be loaded for ntoskrnl.exe
Windows 7 Kernel Version 7600 MP (8 procs) Free x64
Product: WinNt, suite: TerminalServer SingleUserTS Personal
Built by: 7600.16617.amd64fre.win7_gdr.100618-1621
Machine Name:
Kernel base = 0xfffff800`03a65000 PsLoadedModuleList = 0xfffff800`03ca2e50
Debug session time: Sun Dec 19 22:34:27.718 2010 (UTC + 8:00)
System Uptime: 0 days 0:03:01.310
Unable to load image \SystemRoot\system32\ntoskrnl.exe, Win32 error 0n2
*** WARNING: Unable to verify timestamp for ntoskrnl.exe
*** ERROR: Module load completed but symbols could not be loaded for ntoskrnl.exe
Loading Kernel Symbols
...............................................................
................................................................
........................
Loading User Symbols
Loading unloaded module list
......
Unable to load image \SystemRoot\System32\drivers\dxgkrnl.sys, Win32 error 0n2
*** WARNING: Unable to verify timestamp for dxgkrnl.sys
*** ERROR: Module load completed but symbols could not be loaded for dxgkrnl.sys
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* *
* Bugcheck Analysis *
* *
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Use !analyze -v to get detailed debugging information.

BugCheck 116, {fffffa80068054e0, fffff8800377f028, ffffffffc000009a, 4}

Unable to load image \SystemRoot\system32\DRIVERS\nvlddmkm.sys, Win32 error 0n2
*** WARNING: Unable to verify timestamp for nvlddmkm.sys
*** ERROR: Module load completed but symbols could not be loaded for nvlddmkm.sys
***** Kernel symbols are WRONG. Please fix symbols to do analysis.

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*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
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*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
*************************************************************************
*************************************************************************
*** ***
*** ***
*** Your debugger is not using the correct symbols ***
*** ***
*** In order for this command to work properly, your symbol path ***
*** must point to .pdb files that have full type information. ***
*** ***
*** Certain .pdb files (such as the public OS symbols) do not ***
*** contain the required information. Contact the group that ***
*** provided you with these symbols if you need this command to ***
*** work. ***
*** ***
*** Type referenced: nt!_KPRCB ***
*** ***
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Probably caused by : nvlddmkm.sys ( nvlddmkm+75a028 )

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Thx pls help me, !!!!!!! I can't use my computer at all!!