my mac mini wifi is not connected properly

I suspect you have powered of and then back on your router.

Try resetting the SMC and NVRAM/PRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

About NVRAM and PRAM

Try disconnecting all unnecessary peripherals from the Mini as a test

Try moving the Mini to another location as a test

Try creating a new network location

http://macs.about.com/od/networking/qt/networklocation.htm

Backup your data and install the Combo update

OS X Lion Update 10.7.5 (Client Combo)

OS X Yosemite 10.10.3 Combo Update

OS X Mavericks 10.9.5 Update (Combo)

OS X Mountain Lion Update v10.8.5 (Combo)