cant select serial

Hi My arduino does not shows arduinos serial port in serial port selector. I tried to reinstall arduino, installation cant be finished, device cannot start. I have another arduino replacing new ones bootloader chip does not help. Please tell me if there is a way to fix my arduino! My english is bad.

You do not provide sufficient information.

I have arduino UNO Windows XP My usual serial port is COM11(now its not working) New arduinos port is COM10.