Answer 1

Assuming that you are using the .NET SerialPort class in your application, think about instantiating the class in a try block, so failures can be handled by your applcation.

Check here for useful properties and methods:

http://msdn.microsoft.com/en-us/library/system.io.ports.serialport_members(v=VS.90).aspx

As far as closing a serial  port is concerned, unless your application successfully opened  it, don't. In a multitasking OS, an application that tries to take resources in use will not be well received.

Answer 2

Thanx a lot for your guide......

Regards,

Junaid Manzoor