Switch/Router problems for XP & Win7

Hi there. I'm just a newbie here, and I really need some help.

Before, I have no problems with sharing internet connection between my laptop (Windows 7) and desktop (XP). I'm only using a D-Link Switch to share the connection, plugging both units and modem on the switch, then setting up a small home network. After relying to that kind of setup for years, just recently (maybe a month ago), I started encountering this problem.

My small home network is now unable to share connection. It's either I have connection at my desktop and no connection (limited connectivity) with my laptop, or vice versa. It's really hard because, of course, I can't use both units at the same time to connect to internet. Another is that I need to reset/switch the modem on and off in order to "transfer" the connection from one unit to another.

Hope you can help me with this problem... :)

Can you try the below fix for the Win 7 machine that can't access from XP:

On the Windows 7 machine navigate to the following registry key.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
create or modify 32-bit DWORD: LocalAccountTokenFilterPolicy
set the value to: 1

You don't need to use static IP's to fix this type of problem, use DHCP, it works fine for me in every situation.