Constant BSOD

Here (hopefully) is an English link to Video memory test. I've not heard of this one before but looks good. It appeared to have 254 tests it does, so perhaps you should let it finish.
For Furmark if you see no anomalies or artifacts with the donut after the GPU temp stabilese, your should be done. It ususally takes 10-20 minutes.
Google Translate

Code:

*******************************************************************************
*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *
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Use !analyze -v to get detailed debugging information.

BugCheck C9, {228, fffff88007737e80, fffff98010ec6a60, 0}

*** ERROR: Symbol file could not be found.  Defaulted to export symbols for USBPORT.SYS - 
Unable to load image FNETTBOH_305.SYS, Win32 error 0n2
*** WARNING: Unable to verify timestamp for FNETTBOH_305.SYS
*** ERROR: Module load completed but symbols could not be loaded for FNETTBOH_305.SYS
Probably caused by : FNETTBOH_305.SYS ( FNETTBOH_305+3e80 )

Followup: MachineOwner
---------

0: kd> !analyze -v
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*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *
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DRIVER_VERIFIER_IOMANAGER_VIOLATION (c9)
The IO manager has caught a misbehaving driver.
Arguments:
Arg1: 0000000000000228, A driver's completion routine has not marked the IRP pending if the
	PendingReturned field was set in the IRP passed to it. This may cause the OS
	to hang, especially if an error is returned by the stack.
Arg2: fffff88007737e80, The address in the driver's code where the error was detected.
Arg3: fffff98010ec6a60, IRP address.
Arg4: 0000000000000000

Debugging Details:
------------------


BUGCHECK_STR:  0xc9_228

DRIVER_VERIFIER_IO_VIOLATION_TYPE:  228

FAULTING_IP: 
FNETTBOH_305+3e80
fffff880`07737e80 4533c9          xor     r9d,r9d

FOLLOWUP_IP: 
FNETTBOH_305+3e80
fffff880`07737e80 4533c9          xor     r9d,r9d

IRP_ADDRESS:  fffff98010ec6a60

DEVICE_OBJECT: fffffa8009f58950

CUSTOMER_CRASH_COUNT:  1

DEFAULT_BUCKET_ID:  WIN7_DRIVER_FAULT

PROCESS_NAME:  System

CURRENT_IRQL:  2

TAG_NOT_DEFINED_c000000f:  FFFFF80000BA2FB0

LAST_CONTROL_TRANSFER:  from fffff800035073dc to fffff80003080fc0

STACK_TEXT:  
fffff800`00b9c658 fffff800`035073dc : 00000000`000000c9 00000000`00000228 fffff880`07737e80 fffff980`10ec6a60 : nt!KeBugCheckEx
fffff800`00b9c660 fffff800`0351147a : fffff800`035059f0 fffff880`07737e80 fffff980`10ec6a60 00000000`00000000 : nt!VerifierBugCheckIfAppropriate+0x3c
fffff800`00b9c6a0 fffff800`03512483 : 00000000`00000228 fffff880`07737e80 fffff980`10ec6a60 00000000`ffffffff : nt!ViErrorFinishReport+0xda
fffff800`00b9c6f0 fffff800`03512654 : fffff880`07737e80 fffffa80`0aa6d750 fffff880`07737e80 fffff980`10ec6a60 : nt!VfErrorReport1+0x63
fffff800`00b9c790 fffff800`035255f9 : fffff980`10ec6db8 00000000`00000000 fffff800`00b9c960 fffff980`10ec6a60 : nt!IovpCompleteRequest4+0x64
fffff800`00b9c7c0 fffff800`030849c1 : fffff980`10ec6dbb 00000000`00000000 00000000`00000000 fffff800`0313bc8b : nt!IovpLocalCompletionRoutine+0x189
fffff800`00b9c820 fffff800`0351d19f : fffff980`10ec6a60 fffffa80`0ac5e300 fffffa80`099e1000 00000000`00000000 : nt!IopfCompleteRequest+0x341
fffff800`00b9c910 fffff880`06365631 : fffffa80`099e1050 fffffa80`09f5ac02 00000000`00000002 fffffa80`099e1050 : nt!IovCompleteRequest+0x19f
fffff800`00b9c9e0 fffff880`06365b0f : fffffa80`0ac64702 fffff980`10ec6a60 00000000`ffffffff fffffa80`099e1eb0 : USBPORT+0x13631
fffff800`00b9cac0 fffff880`0636366f : fffffa80`099e1eb0 fffffa80`099e11a0 fffffa80`099e2050 00000000`00000000 : USBPORT+0x13b0f
fffff800`00b9cb20 fffff880`06354f89 : fffffa80`099e1050 00000000`00000000 fffffa80`099e1e02 fffffa80`099e1eb0 : USBPORT+0x1166f
fffff800`00b9cb60 fffff800`0308b6ec : fffff800`031f3e80 fffffa80`099e1eb0 fffffa80`099e1ec8 00000000`00000000 : USBPORT+0x2f89
fffff800`00b9cb90 fffff800`03078cca : fffff800`031f3e80 fffff800`03201cc0 00000000`00000000 fffff880`06354db0 : nt!KiRetireDpcList+0x1bc
fffff800`00b9cc40 00000000`00000000 : fffff800`00b9d000 fffff800`00b97000 fffff800`00b9cc00 00000000`00000000 : nt!KiIdleLoop+0x5a


STACK_COMMAND:  .bugcheck ; kb

SYMBOL_NAME:  FNETTBOH_305+3e80

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: FNETTBOH_305

IMAGE_NAME:  FNETTBOH_305.SYS

DEBUG_FLR_IMAGE_TIMESTAMP:  4cd1001a

FAILURE_BUCKET_ID:  X64_0xc9_228_FNETTBOH_305+3e80

BUCKET_ID:  X64_0xc9_228_FNETTBOH_305+3e80

Followup: MachineOwner
---------

0: kd> lmvm FNETTBOH_305
start             end                 module name
fffff880`07734000 fffff880`07741000   FNETTBOH_305 T (no symbols)           
    Loaded symbol image file: FNETTBOH_305.SYS
    Image path: FNETTBOH_305.SYS
    Image name: FNETTBOH_305.SYS
    Timestamp:        Wed Nov 03 12:24:26 2010 (4CD1001A)
    CheckSum:         00008787
    ImageSize:        0000D000
    Translations:     0000.04b0 0000.04e4 0409.04b0 0409.04e4
0: kd> !sysinfo cpuspeed
sysinfo: could not find necessary interfaces.
sysinfo: note that mssmbios.sys must be loaded (XPSP2+).

Most likely an FNet or XFastUSB driver (AsRock)
Description here: Driver Reference Table - FNETTBOH_305.SYS

I'd recommend uninstalling this app completely and disable verifier.

See if you still get BSOD-s.