Serial Port Communication problem in windows 7 64 bit

Question

Hi,
   We have a device which will communicate the application through com port.We are able to send commands to the device and receive responses from the device.But recently we upgraded to windows 7 64 bit machines we are facing weird problem.The data is never received in this mode of machine.In other words the OnReceive event or OnComm event never fires in windows 7 64 bit machine.It works fine in xp and windows 7 32 bit machine.We tried the serial port communicatin using .Net serial port class and some third party tools and even with the hyperterminal.We only have receive problem.
 
We tried all options such as
1)Installing with admin privilleges.
2)Regitering controls.
3)Enabling Rtstrheshold and rts to receive data but all failed.
4)Updated drivers.

Please can any one suggest some steps to work out this scenario in windows 7 64 bit machine.

Thanks
Pkkrao.