Wierd Problem - Network adapter acting like being unplugged everyfew seconds

hey guys, im currently have connected to my computer a windows xp machine, everything was working fine untill yeterday, now the computer is unable to connect to me and vice vera, but the odd thing is the network keeps thinking the cables being unpluged and repluged every few seconds, and when i go to network connections, the icon keeps flashing the red Cross ontop of the network device.

when the other computer is connected directly into the modem, it works fine
i am running windows vista ulimate 32bit, the other machine is running windows xp pro sp 3.

How did you set up your network ?

what do you mean exactly,
the netwok is austmatically set up in vista, and in xp, just normally as a home network