Studio 1555 fails to connect to visible wireless networks

I'm troubleshooting my Dad's Studio 1555 laptop (running windows 7 x64). According to device manager it has an "Intel WiFi Link 5100 AGN" adapter (driver v 14.3.2.1). The laptop has been able to connect to wireless networks in the past, and to our home network specifically, but a few weeks ago stopped being able to connect to any network. We have tried connecting to several networks, all of which work fine with other devices.

This is the presentation:

1. We see the wireless network and connect to it.

2. We connect to the network and enter the security key, and the connection prompt disappears.

3. A moment later windows prompt us: "Windows was unable to connect to (network name)". The intel wireless event viewer just says "Connection Attempt Fail"

I wasn't around, so I'm not sure if anything precipitated this. A few things I've checked:

1. System and router reboot.
2. Manually updated wireless drivers as specified by Dell and Intel (deleted and reinstalled device)
3. Verified all required windows updates installed
4. Full virus and malware checks (McaFee Internet Security, Malwarebytes, Spybot)
5. Verified DHCP settings are correct.
6. Verified router settings (but it doesn't work on other networks, so it's probably not that).

I have a lot of troubleshooting experience but this one has me stumped. I'd appreciate any tips people could give me. Thanks,

Matt