MacBook Air 2011 cannot connect to Wi-Fi properly after repair

Question

Hi,
Recently I took my 2011 MacBook Air into an Apple Store where they replaced the SSD with a fresh one loaded with Mavericks. When I started it up in the Apple Store it found their local Wi-Fi properly. However, when I try to connect it to my Wi-Fi at home (with WPA2E security), it does not work properly.
The symptoms are rather strange: it appears to connect to DHCP on the router and receive an IP address. I've tried changing the IP address on the DHCP server and the IP on the MacBook Air changes appropriately so it is getting a proper DHCP connection and the data recieved is correct. However after this it is unable to actually do anything on the network. It can't even ping the router at 192.168.1.1, and everything else fails for lack of DNS.
When I try to use Network Diagnostics it acts rather strangely - it asks me several times for my Wi-Fi password, then the lights turn green up until "ISP" which remains red. Then, all three lower lights turn green for a moment and Diagnostics gives the message "your internet connection is working properly" even though the lights from ISP down all turn red again straight away. Because of the odd password behaviour I tried enabling the "allow all applications to access this" option in Keychain Access, but this didn't change anything.
Does anyone know how to fix this?

Answer 1

Hi hyperphase,
Thanks for visiting Apple Support Communities.
If you're not able to connect to the internet or your router at home, you may want to use the steps quoted below, and check the settings against those mentioned in this article:
iOS and OS X: Recommended settings for Wi-Fi routers and access points
http://support.apple.com/kb/ht4199
Before configuring or adjusting specific settings, perform the following steps:
Ensure that your Wi–Fi router's firmware is up to date.
If you are using a Wi–Fi base station, refer to this article for information on how to update it.
Verify that all Wi–Fi devices you intend to use support the settings recommended in this article.
If possible, back up your current Wi–Fi router's settings.
If necessary, refer to the product documentation or manufacturer's website.
Forget or remove the Wi-Fi settings for your network from any devices that connect to your Wi-Fi router. (This will prevent the devices from attempting to connect to your network with the old configuration.) You will need to reconnect these devices to your network once you've finished applying the new settings.
Configure all Wi–Fi base stations on the same network with the same settings. Not doing so will cause connectivity and reliability issues. On dual-band Wi–Fi base stations, configure both bands to have the same settings unless otherwise noted below.
All the best,
Jeremy