It depends on the type of failure ... if its a physical issue, such as a loose or broken connection, it shouldn't affect the entire motherboard. However, if the particular port controller chip is going bad or is defective (you will eventually see future failure on additional ports of the same type) then its a good idea to replace it.
Also, if it is a port that you only have one of, such as a VGA port, LPT port, etc, you will be better off finding an add-on card that plugs into your PCI slots, rather than going through the trouble of replacing a motherboard, unless you are under warranty of course.
You can replace your LAN port with a wireless card if you have an ASUS P9X79 motherboard. However, it's a better idea to get a card that fits in a USB port so you can keep your LAN port.
You can not change the processor port on a motherboard, you can change the processor to another with the same pin set, but not the port itself. If you want to use a diffrent processor you would need to replace the motherboard with one that supports the pin set of the new processor.
It is the Accelerated Graphics Port on a motherboard for attaching graphics cards.
a port for the IDE cable to connect the hardrive and cddrive to the motherboard.
The expansion card
If your not using it then don't worry about it. But motherboards don't come with a modem port. A modem port is on an add on card like a PCI Modem. Take out the old one and insert another and load the drivers from the included CD that is the cheapest way.
usb
See what COM defines is the communication ports and hence COM 1 is one of the USB port or might be some COM ports you have on your motherboard back. You can refer to the map of your motherboard to know which is the. port for COM 1.
The port can be enabled or disabled through the CMOS setup.
a. Replace the motherboard. b. Disable the modem port and install a modem card in an expansion slot. c. Use an external modem that connects to the serial or USB port. d. Return the motherboard to the factory for repair. If the motherboard is important, replace the motherboard. Other components may be failing and undetected. If the motherboard isn't in a critical piece of hardware, I would simply turn the modem off in the BIOS and add a new modem in an expansion slot.
Check the connections from the usb slot to your motherboard, could be a faulty port or a faulty motherboard connection
No, Memory slots are on the motherboard bus.