Windows 2008 server r2, is giving Network problem..like Sometimes, Server Rejecting Request?

Dear Friends,

One of my client using IBM server with WINDOWS SERVER 2008 r2 Standard 64 Bit VERSION,

In this Two network cards, One is for LAN Modem and other for Internet Router.Both are InNetwork Bridge.

It was working fine, But i Installed Oracle 11g 32bit on the server.and running Application Using Oracle DB.

My Problem is Sometimes, Server Rejecting Requests. Only few seconds.Then Automatically my workstation All Type of applications(Excel, Oracle Application , MS Dos Application..) are stopped.After Few minutes it was ok. But It is in frequent event.

I Can not understand what may be the problem.

I UnInstalled all virus guards and firewall also.

But Other clients using same type environment(Without network bridge), all are working fine.

Please any expects help me.