Verify that the IP you see on the TV screen is the correct one (as hdld_svr.elf uses somewhat different config file, compared to other homebrew). Check if ping works. Check if you can connect using hdl_dump (that is the command-line tool). Check if there is network traffic going on and for how long, after you click Attach button (by wathing the led or by using Task Manager). Network sniffer is your friend, if you know how to use one. If you have messed-up partitions, hdl_dump might gone into an infinite loop.
"Only those who try will become." -- Kimahri Ronso