"Symbols can not be loaded" when trying to read dump
I usually go to the System control panel, then Advanced tab, then Environment. You can then add the requisite _NT_SYMBOL_PATH variable. Then you don't have to do anything on the command-line before running WinDbg.
The setting of srv*C:\Windows\Symbols*http://msdl.microsoft.com/download/symbols as suggested by staffan is fine. I usually prefer to use my own profile for storing symbols though (so that I don't need to edit the permissions for C:\Windows\Symbols, since I intentionally run as a limited user, for good security hygiene). Thus (in my case) my _NT_SYMBOL_PATH is srv*C:\Documents and Settings\cky\symbols*http://msdl.microsoft.com/download/symbols.
Hope this helps. :-)
Quick answer is to
c:\> set _NT_SYMBOL_PATH=SRV*C:\WINDOWS\Symbols*http://msdl.microsoft.com/download/symbols
before starting windbg.
Quicker answer:
!symfixBut it only affects the current windbg/ntsd/cdb/kd.