Dear All,
I am facing problem with Network cards.
We have 2 systems which is connected to each other via network switch .Each network stop working after a time(time
& day is not fixed). Its occurs with each lan cards separately at different time & day .Some times its start working after restarting its services or disconnecting and connecting LAN cable.
but this happen again and again irregularly . So,Kindly suggest me any solution.

I think it's a hardware problem.
did you try to replace your lan cards?

I'd replace the switch before replacing the LAN cards. I mean it's highly unlikely that two systems would have the same harware problem on the same network at the same time. But you never know...

Before replacing any hardware, I'd start looking at stuff like:
logs for the switch (if any are available) - you didn't mention what type hardware you're using, but sometimes you can find errors there.
DNS (are your IP leases set to some rediculous setting and/or are you DNS server(s) reliable - do you have an IP conflict on your network?).

The fact that you mentioned disconnecting/reconnecting the network cable should be a clue. Does hardware fix itself be being unplugged/plugged? Not usually. So I'd look for a software/protocol problem before I started blaming the hardware. Of course if you have spare hardware, feel free to experiment.