BSOD Probably caused by : win32k.sys, help!

Hello, I have been occasionally getting bsods on my computer, at random times, and am not sure why, it seems somewhat unlikely to be a driver problem, and I think I may be having hardware issues! Any help would be greatly appreciated, and attached you will find my 3 minidumps i have received as a result of the BSODs.

PC:
Mobo: Gigabyte MA770-UD3
Ram: 2gb (2x1) PQI turbo DDR2 800
GPU: ATI 3870 manufactured by Saphire
PSU: 500w Apevia
CPU: AMD Kuma 7850 @ 2.8ghz
HDD: WD 250gb SATA
Optical: LG DVD burner

OS:
Windows Vista Ultimate x64 SP 2

Here are the minidump results:

*******************************************************************************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
Use !analyze -v to get detailed debugging information.
BugCheck 3B, {c0000005, fffff9600013f090, fffffa600941ef70, 0}
Probably caused by : win32k.sys ( win32k!PFEOBJ::vFreepfdg+e8 )
Followup: MachineOwner
---------
0: kd> !analyze -v
*******************************************************************************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
SYSTEM_SERVICE_EXCEPTION (3b)
An exception happened while executing a system service routine.
Arguments:
Arg1: 00000000c0000005, Exception code that caused the bugcheck
Arg2: fffff9600013f090, Address of the exception record for the exception that caused the bugcheck
Arg3: fffffa600941ef70, Address of the context record for the exception that caused the bugcheck
Arg4: 0000000000000000, zero.
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!PFEOBJ::vFreepfdg+e8
fffff960`0013f090 0fba60300f bt dword ptr [rax+30h],0Fh
CONTEXT: fffffa600941ef70 -- (.cxr 0xfffffa600941ef70)
rax=f9e03a2800000161 rbx=0000000000000000 rcx=fffff900c299e910
rdx=fffffa8004697ca0 rsi=fffff900c0652a40 rdi=fffffa600941f820
rip=fffff9600013f090 rsp=fffffa600941f7d0 rbp=0000000000000000
r8=0000000000000000 r9=0000000000000000 r10=0000000000000000
r11=fffffa8002a723d0 r12=0000000000000000 r13=0000000000000000
r14=000000000000181f r15=0000000000000001
iopl=0 nv up ei ng nz na pe cy
cs=0010 ss=0018 ds=002b es=002b fs=0053 gs=002b efl=00010283
win32k!PFEOBJ::vFreepfdg+0xe8:
fffff960`0013f090 0fba60300f bt dword ptr [rax+30h],0Fh ds:002b:f9e03a28`00000191=????????
Resetting default scope
CUSTOMER_CRASH_COUNT: 1
DEFAULT_BUCKET_ID: VISTA_DRIVER_FAULT
BUGCHECK_STR: 0x3B
PROCESS_NAME: left4dead.exe
CURRENT_IRQL: 0
LAST_CONTROL_TRANSFER: from fffff960002ffa9c to fffff9600013f090
STACK_TEXT:
fffffa60`0941f7d0 fffff960`002ffa9c : 00000000`00000000 fffffa80`04697c70 00000000`00000001 00000000`746e6647 : win32k!PFEOBJ::vFreepfdg+0xe8
fffffa60`0941f800 fffff960`0030a07f : 00000000`00000000 fffff900`c009a540 fffff900`c000a010 00000000`00000000 : win32k!RFONTOBJ::vDeleteRFONT+0x210
fffffa60`0941f860 fffff960`00309cf6 : 00000000`00000000 fffff900`c0674010 fffff900`c327ba10 fffff900`c0175ca0 : win32k!vRestartKillRFONTList+0xab
fffffa60`0941f8b0 fffff960`001b91a2 : fffff900`c2140a58 00000000`00000000 00000000`00000000 fffff900`0000000d : win32k!PFTOBJ::bUnloadWorkhorse+0x196
fffffa60`0941f930 fffff960`001b9d85 : fffff900`c2140a30 00000000`00000000 00000000`00000001 00000000`00000001 : win32k!vCleanupPrivateFonts+0x72
fffffa60`0941f970 fffff960`001ae234 : 00000000`00000000 00000000`00000000 fffff900`c0840010 00000000`ffffffff : win32k!NtGdiCloseProcess+0x479
fffffa60`0941f9d0 fffff960`001adaab : 00000000`00000000 fffff900`c0840010 00000000`00000000 00000000`00000000 : win32k!GdiProcessCallout+0x1f4
fffffa60`0941fa50 fffff800`023039c4 : 00000000`00000000 00000000`00000000 00000000`00000000 fffffa80`02a723d0 : win32k!W32pProcessCallout+0x6f
fffffa60`0941fa80 fffff800`02305ee9 : 00000000`00000000 fffffa80`02a72301 00000000`00000000 00000000`00000000 : nt!PspExitThread+0x41c
fffffa60`0941fb70 fffff800`022f6f72 : 00000000`00000000 00000000`0000000c 00000000`7efdd000 fffff880`0000000c : nt!PspTerminateThreadByPointer+0x4d
fffffa60`0941fbc0 fffff800`020aaef3 : fffffa80`02330c10 fffffa80`02a723d0 fffffa60`0941fca0 00000000`7efdd000 : nt!NtTerminateProcess+0xfa
fffffa60`0941fc20 00000000`779a6fda : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : nt!KiSystemServiceCopyEnd+0x13
00000000`0007e588 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x779a6fda

FOLLOWUP_IP:
win32k!PFEOBJ::vFreepfdg+e8
fffff960`0013f090 0fba60300f bt dword ptr [rax+30h],0Fh
SYMBOL_STACK_INDEX: 0
SYMBOL_NAME: win32k!PFEOBJ::vFreepfdg+e8
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: win32k
IMAGE_NAME: win32k.sys
DEBUG_FLR_IMAGE_TIMESTAMP: 49edb61d
STACK_COMMAND: .cxr 0xfffffa600941ef70 ; kb
FAILURE_BUCKET_ID: X64_0x3B_win32k!PFEOBJ::vFreepfdg+e8
BUCKET_ID: X64_0x3B_win32k!PFEOBJ::vFreepfdg+e8
Followup: MachineOwner
---------

Since you were playing Left 4 Dead at the Time have you overclocked any of your hardware? Try returning to stock levels if you have. Since its win32k.sys, check your hard drive for errors and especially the memory

I was overclocked slightly at the time, and immediately after my computer reset after the bsod, i did lower the clock back to factory (from 3.0 to 2.8), i had a feeling that it was potentially something to do with the overclock, just didn't expect a bsod upon leaving the game, as i had played for well over an hour and got the dump after exiting the game. I have yet to experience another, so I am thinking that may have been it. Thanks for taking the time to look at my minidump, I too, checked the debug report, but as technically inclined as I may be, this is actually the first BSOD i have had in years of building/ocing pcs. Thanks again!

btw, reset my slight overclock and have had no problems with memory dumps since, needless to say, I feel like such a n00b.

I'm glad that you were able to fix it!
Thanks for letting us know!