Get them quite often, more often while playing World of Warcraft

I've had a few performances problems with my pc for a while but the past month or so i've been getting BSOD's more often than seems normal. It's usually when i'm on a game like World of Warcraft but many times when i'm just sitting there doing nothing so it's quite weird. Most of the time my screen freezes, goes black then pc restarts itself instantly (i assume this is normal BSOD).

I have quite a few dumpfiles but didn't know if you wanted all as they're pretty much exactly the same.

On Thu 07/11/2013 22:44:44 GMT your computer crashed
crash dump file: C:\Windows\Minidump\110713-27424-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x4A4F4C)
Bugcheck code: 0x124 (0x0, 0xFFFFFA80050D2038, 0x0, 0x0)
Error: WHEA_UNCORRECTABLE_ERROR
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This bug check indicates that a fatal hardware error has occurred. This bug check uses the error data that is provided by the Windows Hardware Error Architecture (WHEA).
This is likely to be caused by a hardware problem problem. This problem might be caused by a thermal issue.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver that cannot be identified at this time.

On Wed 06/11/2013 07:25:20 GMT your computer crashed
crash dump file: C:\Windows\Minidump\110613-22869-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x4A4F4C)
Bugcheck code: 0x124 (0x0, 0xFFFFFA80050B0038, 0x0, 0x0)
Error: WHEA_UNCORRECTABLE_ERROR
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This bug check indicates that a fatal hardware error has occurred. This bug check uses the error data that is provided by the Windows Hardware Error Architecture (WHEA).
This is likely to be caused by a hardware problem problem. This problem might be caused by a thermal issue.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver that cannot be identified at this time.

Sorry if i haven't given enough information, just trying to avoid a full reformat and as i said i've been getting performance issues the past few months but not sure if it's related. I used to be able to play a game like Diablo 3 on best settings and watch a HD tv show on other screen, now i don't use the other screen at all as my pc goes noticeably slower and cant play games like Diablo on best settings even on 1 screen.

Please follow - Blue Screen of Death (BSOD) Posting Instructions