srienstr (8/8/2013)
select checksum('00000000-0000-0000-0000-000000000000')-1448389036
You're calculating the checksum of a value that just happens to loook remarkably like a uniqueidentifier value - but is just a plain old varchar.
select checksum(cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) )
Result: 0
(on my system)