I have a Dell Latitude C540/C640. Could you please let me know how I turn on the wireless on this computer?
Laptops with Built-in Wireless Adapters
Many laptops come with built-in wireless adapters, but it appears that the Dell Latitude C540/C640 may not. I downloaded the user's manual and didn't find any mention of a built-in wireless adapter. Look on the laptop itself for a small on/off slider or wheel labeled "wireless" or "Wi-Fi" as that's how most built-in adapters appear. The switch or wheel would likely be mounted along the edges of the laptop.
However, it's doubtful that your computer has an onboard WiFi adapter. Try going to Control Panel > Device Manager and then clicking on Network Adapters. Any adapters listed other than an Ethernet controller? Anything with the words "wireless" or "Wi-Fi" listed?
You can also go to Control Panel > Network Connections and see if a wireless adapter is listed. If so, try right-clicking the adapter and seeing if any options for enabling the card are listed.
PCI Wireless Adapters
While it's doubtful that this particular laptop has wireless built in, you're not necessarily out of luck. The user's guide says that it has a Type IIIA mini PCI card slot with Wi-Fi wireless support. This means that you can buy a wireless PCI card and insert it into the slot on your computer. It looks like the PCI card slot is located on the left side of your computer toward the screen.
Installing PCI wireless cards is generally a simple matter of inserting the card into the slot and allowing Windows to recognize the device and load the appropriate device drivers. You will need to configure the card to connect to your home's wireless network. Prices range anywhere from about $20 to over $100.