Take out the space (unless you are looking for lines with just one space)
^$
So, given a file called test.txt, JUST the sed part would be:
sed '/^$/d' test.txt
thines01
Postaholic
2,424 posts since Oct 2009
Reputation Points: 445
Solved Threads: 402
...or if you just want to do it from the command-line
perl -pi -e "s/^\n//" test.txt
thines01
Postaholic
2,424 posts since Oct 2009
Reputation Points: 445
Solved Threads: 402