I used who crashed and this is what it says
Crash Dump Analysis
Crash dump directory: C:\Windows\Minidump
Crash dumps are enabled on your computer.
On Sun 4/28/2013 5:12:08 PM GMT your computer crashed
crash dump file: C:\Windows\Minidump\042813-19328-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x71F00)
Bugcheck code: 0x50 (0xFFFFF8A009B66000, 0x0, 0xFFFFF80003139079, 0x0)
Error: PAGE_FAULT_IN_NONPAGED_AREA
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This indicates that invalid system memory has been referenced.
This appears to be a typical software driver bug and is not likely to be caused by a hardware problem.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver that cannot be identified at this time.
On Sun 4/28/2013 5:12:08 PM GMT your computer crashed
crash dump file: C:\Windows\memory.dmp
This was probably caused by the following module: aswsnx.sys (aswSnx+0x27803)
Bugcheck code: 0x50 (0xFFFFF8A009B66000, 0x0, 0xFFFFF80003139079, 0x0)
Error: PAGE_FAULT_IN_NONPAGED_AREA
file path: C:\Windows\system32\drivers\aswsnx.sys
product: avast! Antivirus
company: AVAST Software
description: avast! Virtualization Driver
Bug check description: This indicates that invalid system memory has been referenced.
This appears to be a typical software driver bug and is not likely to be caused by a hardware problem.
A third party driver was identified as the probable root cause of this system error. It is suggested you look for an update for the following driver: aswsnx.sys (avast! Virtualization Driver, AVAST Software).
Google query: AVAST Software PAGE_FAULT_IN_NONPAGED_AREA