Initially I thought it might have been a driver (expecting the usual ati) then I considered the new ram, but it passes every test I can throw at it so I'm back at square one i.e. lack of windows knowledge hoping I haven't corrupted windows 
Debugging tool produced this, can anyone expand on it
I was planning on reinstalling this week anyway, just don't want to recreate my problem.

Debugging tool produced this, can anyone expand on it

Code:
Microsoft (R) Windows Debugger Version 6.12.0002.633 AMD64
Copyright (c) Microsoft Corporation. All rights reserved.
Loading Dump File [C:\Windows\Minidump\093011-31871-01.dmp]
Mini Kernel Dump File: Only registers and stack trace are available
Symbol search path is: SRV*C:\SymCache*http://msdl.microsoft.com/download/symbols
Executable search path is:
Windows 7 Kernel Version 7601 (Service Pack 1) MP (4 procs) Free x64
Product: WinNt, suite: TerminalServer SingleUserTS Personal
Built by: 7601.17640.amd64fre.win7sp1_gdr.110622-1506
Machine Name:
Kernel base = 0xfffff800`02e16000 PsLoadedModuleList = 0xfffff800`0305b670
Debug session time: Fri Sep 30 16:01:40.802 2011 (UTC + 1:00)
System Uptime: 0 days 6:18:04.223
Loading Kernel Symbols
...............................................................
................................................................
......................................
Loading User Symbols
Loading unloaded module list
.....
*******************************************************************************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
Use !analyze -v to get detailed debugging information.
BugCheck 1E, {ffffffffc0000005, fffff960000de2de, 0, ffffffffffffffff}
Probably caused by : partmgr.sys ( partmgr!PmGlobalDispatch+9f )
Followup: MachineOwner
---------
0: kd> !analyze -v
*******************************************************************************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
KMODE_EXCEPTION_NOT_HANDLED (1e)
This is a very common bugcheck. Usually the exception address pinpoints
the driver/function that caused the problem. Always note this address
as well as the link date of the driver/image that contains this address.
Arguments:
Arg1: ffffffffc0000005, The exception code that was not handled
Arg2: fffff960000de2de, The address that the exception occurred at
Arg3: 0000000000000000, Parameter 0 of the exception
Arg4: ffffffffffffffff, Parameter 1 of the exception
Debugging Details:
------------------
EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%08lx referenced memory at 0x%08lx. The memory could not be %s.
FAULTING_IP:
win32k!MultiUserGreCleanupHmgOwnRemoveAllLocks+72
fffff960`000de2de 44896008 mov dword ptr [rax+8],r12d
EXCEPTION_PARAMETER1: 0000000000000000
EXCEPTION_PARAMETER2: ffffffffffffffff
READ_ADDRESS: GetPointerFromAddress: unable to read from fffff800030c5100
ffffffffffffffff
ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%08lx referenced memory at 0x%08lx. The memory could not be %s.
BUGCHECK_STR: 0x1E_c0000005
CUSTOMER_CRASH_COUNT: 1
DEFAULT_BUCKET_ID: VISTA_DRIVER_FAULT
PROCESS_NAME: Steam.exe
CURRENT_IRQL: 0
LAST_CONTROL_TRANSFER: from fffff80002ede588 to fffff80002e92c40
STACK_TEXT:
fffff880`09703858 fffff800`02ede588 : 00000000`0000001e ffffffff`c0000005 fffff960`000de2de 00000000`00000000 : nt!KeBugCheckEx
fffff880`09703860 fffff800`02e922c2 : fffff880`09704038 00000000`00017b68 fffff880`097040e0 00000000`00000fcf : nt! ?? ::FNODOBFM::`string'+0x4977d
fffff880`09703f00 fffff800`02e90bca : 00000000`000016f4 00000000`00000001 fffffa80`08c66ee0 fffff960`000d5290 : nt!KiExceptionDispatch+0xc2
fffff880`097040e0 fffff960`000de2de : 00000000`00000000 00000000`00000001 00000000`00000001 00000000`00000001 : nt!KiGeneralProtectionFault+0x10a
fffff880`09704270 fffff960`000dda0b : 00000000`00000000 fffff880`0970461f 00000000`00000998 fffff900`c077c010 : win32k!MultiUserGreCleanupHmgOwnRemoveAllLocks+0x72
fffff880`097042a0 fffff960`000d50f0 : 00000000`00000998 fffff880`09704600 fffff900`c077c010 fffff960`00000000 : win32k!NtGdiCloseProcess+0x11b
fffff880`09704300 fffff960`000d4823 : 00000000`00000000 fffff880`097046a0 fffffa80`09882b60 00000000`00000000 : win32k!GdiProcessCallout+0x200
fffff880`09704380 fffff800`03168a81 : 00000000`00000000 00000000`00000000 00000000`00000000 fffffa80`09882b00 : win32k!W32pProcessCallout+0x6b
fffff880`097043b0 fffff800`0314c09d : 00000000`40010004 00000000`00000001 fffff8a0`78457300 fffffa80`0994eb60 : nt!PspExitThread+0x4d1
fffff880`097044b0 fffff800`02e863fa : fffff8a0`c0000034 fffff800`03406ae7 00000000`00920090 00000000`0018a6ec : nt!PsExitSpecialApc+0x1d
fffff880`097044e0 fffff800`02e86740 : 00000000`003cadd8 fffff880`09704560 fffff800`0314c010 00000000`00000001 : nt!KiDeliverApc+0x2ca
fffff880`09704560 fffff800`02e865db : 00000000`003cadd8 00000000`00000000 fffff800`0314c010 00000000`00000000 : nt!KiInitiateUserApc+0x70
fffff880`097046a0 00000000`755a1b68 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : nt!KiApcInterrupt+0x10b
00000000`0018c5c8 fffff800`02e8a210 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x755a1b68
fffff880`09704aa0 fffffa80`07a9ece0 : fffff880`00f940af fffffa80`0a305bd0 00000000`ffffffff fffffa80`0a305e98 : nt!KiCallUserMode
fffff880`09704aa8 fffff880`00f940af : fffffa80`0a305bd0 00000000`ffffffff fffffa80`0a305e98 fffff880`097053f0 : 0xfffffa80`07a9ece0
fffff880`09704ab0 00000000`00000007 : 402832b3`33333333 00000000`00000000 00000000`00000000 00000000`00000000 : partmgr!PmGlobalDispatch+0x9f
fffff880`09704ae0 402832b3`33333333 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x7
fffff880`09704ae8 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x402832b3`33333333
STACK_COMMAND: kb
FOLLOWUP_IP:
partmgr!PmGlobalDispatch+9f
fffff880`00f940af 8bf0 mov esi,eax
SYMBOL_STACK_INDEX: 10
SYMBOL_NAME: partmgr!PmGlobalDispatch+9f
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: partmgr
IMAGE_NAME: partmgr.sys
DEBUG_FLR_IMAGE_TIMESTAMP: 4ce792c0
FAILURE_BUCKET_ID: X64_0x1E_c0000005_partmgr!PmGlobalDispatch+9f
BUCKET_ID: X64_0x1E_c0000005_partmgr!PmGlobalDispatch+9f
Followup: MachineOwner
---------
I was planning on reinstalling this week anyway, just don't want to recreate my problem.