1. Network port failure.

In most laptops the network port (aka RJ-45 port) is soldered directly to the motherboard. If for some reason the network port fails (I’m talking about hardware, not software failure), the whole motherboard has to be replaced.

Instead of replacing the motherboard, you can use a PCMCIA network card (aka LAN PC card). You plug this card into the available PC slot in your laptop and get a network port instead.

2. USB ports failure.

Most laptops have a few USB ports available and if one of them stops working, usually it’s not a big deal because you still have two or three working USB ports left. But what if all of them stopped working at once. Let’s say the USB controller on the motherboard went bad and the laptop stopped recognizing any USB device plugged in any USB port. Again, I’m talking about hardware, not software failure. In order to fix this problem you’ll have to replace the motherboard.

Alternatively, you can use a PCMCIA USB card. You plug this card into the PC slot and get two or four USB ports instead. It depends on the type of your PCMCIA card.

3. Internal wireless (Wi-Fi) card failure.

Most newer laptops come with an internal wireless card installed. In some models the wireless card could be easily access through the door on the bottom of the laptop. In other models, the wireless card is buried deep inside the case. What can you do if the internal wireless card fails? You can replace the internal wireless card with another one or use a PCMCIA wireless card instead.

4. Internal flash memory card reader failure.

Most newer laptops come with an internal memory card reader installed. You can plug most known flash memory cards into the slot and access the content right away. Usually the card reader is soldered directly to the motherboard and if it fails, you have to replace the whole motherboard or use it as is.

If you don’t want to replace the motherboard you can use an external USB flash memory card reader. All you have to do is plug the card reader into the available USB port in your laptop and it’s ready to go.

5. Internal CD/DVD drive failure.

You’ll find an internal CD/DVD optical drive in most laptops. If the optical drive fails and stops reading CDs and DVDs, it has to be replaced with a new one. Internal laptop optical drives are not cheap.

Instead of replacing the internal drive, you can use an external USB optical drive. Simply plug this drive into the USB port, let your laptop detect and install the drive and it’s ready for you. Also, you can use this optical drive with any other computer which is very convenient.

1. Finding part number.
SparePartsWarehouse can help you to find the part number. On this website you can search for notebook parts by vendor. You’ll find part numbers for Compaq, HP, IBM, Sony and Toshiba notebooks.
Select your vendor/model line, choose laptop series and choose the laptop model. After that you can search through the entire list of parts for your laptop or just use the filtering tool to find a particular part. Each part usually has an original part number and an alternative part number. You can use either number. Now, when you know the part number, you can start searching for the best price.

2. Fining inexpensive parts.
First of all, try searching here. You can find a very inexpensive brand new part. If there are no new parts, you can buy a used one. If you cannot find this part on eBay, try searching by the part number on Google. Most likely the search will bring you many results and you will find what you are looking for.
Finally, when you receive the part, you can use laptop service manuals to install it.

UPDATE:
I just started a new project – free laptop repair related classifieds.
You can see this site here: Any Notebook Part
If you are selling new or used laptop parts, used laptops, you can place your ad on this site. It’s free.
You can request parts too, maybe somebody has them for sale.