Little help with Wi-Fi troubleshooting please?

I own a Mac Mini late 2012 and today I noticed that if I enable my Wi-Fi, the Mac Mini does not detect any wireless networks. It's not really a big issue for me since I am constantly connected via Ethernet but I would like to know if there's something I can do to regain wireless functionality.

One thing that pops to my head and could be related is that a few months back, I opened my Mac Mini in order to install a second hard disk. Although I was extremely careful not to break any connectors, I guess it might be possible that something went wrong.

On the other hand, If I had damaged the wi-fi, should't OSX refuse to detect my WiFi card to begin with? When I go to "System Preferences", "Network", I am able to turn on Wi-Fi on without problems, it's just that I can't detect any wireless networks around me whatsoever. I am also pasting the output from wi-fi section of System Information

Software Versions:
CoreWLAN: 5.0 (500.35.2)
CoreWLANKit: 4.0 (400.35)
Menu Extra: 10.0 (1000.33.2)
System Information: 9.0 (900.9)
IO80211 Family: 7.0 (700.52)
Diagnostics: 4.0 (400.68)
AirPort Utility: 6.3.4 (634.17)
Interfaces:
en1:
Card Type: AirPort Extreme (0x14E4, 0x10E)
Firmware Version: Broadcom BCM43xx 1.0 (7.15.124.12.10)
MAC Address: 88:53:95:2c:25:b9
Locale: ETSI
Country Code: X3
Supported PHY Modes: 802.11 a/b/g/n
Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140
Wake On Wireless: Supported
AirDrop: Supported
Status: Not Associated

I have tried all the obvious troubleshooting steps (reboot Mac Mini, reboot Modem/Router, disable Ethernet on Mac Mini, disable and reenable Wireless on the Router but nothing seems to help. Any ideas would be greatly appreciated.

I did try that. However all I'm getting to is a screen where wi-fi is enabled and searching for networks (without finding a single one).

Normally this would be an open and shut case that the wi-fi antenna is disconnected/broken/defective but OS X reports that the wi-fi antenna is present and the OS is able to turn it on and off. Is there something I can do on OS X? I don't know if it's relevant but I upgraded to Yosemite from Maverick instead of performing a clean install. Maybe something went wrong there?

Well, I opened the mini and everything seemed to be in place. Just to make sure, I removed and reattached the antenna connector from its socket and carefully reinstalled the antenna plate. After booting the mini, I am still unable to detect any wireless networks when I turn on Wi-Fi.

Any ideas are more than welcome...