Windows 7 is impressive OS but still it crashes sometimes, and if you've installed diagnostic software like the Windows debugging tools then you need the crash dump file to hand over for further investigation.
And yet in some situations you'll find the memory.dmp file missing.
So why does it happen? couple of reasons find out below.
First, click Start, right-click Computer and select Properties > Advanced System Settings > Startup and Recovery Settings. Make sure that "Write debugging information" is set to something other than "none", and that "Dump file" is the default "%SystemRoot%\MEMORY.DMP".
If that's all correct then check your free hard drive space. If your system isn't on a domain, and has less than 25GB free space, then Windows 7 will no longer keep a crash dump file.
If you'd like to change that, launch REGEDIT, browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\CrashControl, create a new DWORD value called AlwaysKeepMemoryDump, set it to 1, and in future the crash dump file will always be preserved.