TCPIP does screwy things like this. You might want to try the command
prompt ipreset and winsock reset.

Parts of the MS pages follow:
The reset command is available in the IP context of the NetShell
utility. Follow these steps
to use the reset command to reset TCP/IP manually:
To open a command prompt, click Start and then click Run. Copy and paste
(or type) the
following command in the Open box and then press ENTER:
cmd
At the command prompt, copy and paste (or type) the following command
and then press ENTER:
netsh int ip reset c:\resetlog.txt
Note If you do not want to specify a directory path for the log file,
use the following
command:
netsh int ip reset resetlog.txt
Reboot the computer.
When you run the reset command, it rewrites two registry keys that are
used by TCP/IP. This
has the same result as removing and reinstalling the protocol. The reset
command rewrites
the following two registry keys:
SYSTEM\CurrentControlSet\Services\Tcpip\Parameters \
SYSTEM\CurrentControlSet\Services\DHCP\Parameters\

Manual steps to recover from Winsock2 corruption
Windows XP with Service Pack 2 instructions
To repair Winsock if you have Windows XP Service Pack 2 (SP2) installed,

type netsh winsock reset at the command prompt, and then press ENTER.