Q: wifi having problems

Unfortunately, it is a common issue.

OSX Yosemite Wifi issues

Take a look at this article, hope it will help you (these steps work for OS X 10.10.3 as well):

http://osxdaily.com/2015/01/30/os-x-10-10-2-yosemite-wi-fi-problems/

How are you connected to the net? 

Are you having problems while being connected through ethernet as well as wireless?

If you are not having problems using the ethernet, you should use your iMac that way instead of wireless.

To troubleshoot when wireless try all of the following suggestions:

Try the basics first:

  Change your router channel number.  Most times this works & is all you have to do.

Disconnect & reconnect your modem.  unplug it for about 10 seconds.  Plug it back in.  Do the same for Apple’s routers.  Wait for everything to reboot.

System Preferences>Network

Click the Assist Me button.

In the next window that pops up, click the Diagnostic button & do the necessary.

Research Knowledge Base for network problems that pertain to the OS that is currently installed on your computer.  See these basic networking KB Articles:  http://support.apple.com/kb/HT1401 AirPort troubleshooting guide

http://support.apple.com/kb/HT4628  Wi-Fi: How to troubleshoot Wi-Fi connectivity

http://support.apple.com/kb/HT2712 Using network locations in Mac OS X

Manually provided DNS server addresses are higher priority than DHCP's

http://support.apple.com/kb/HT1714 Solutions for connecting to the Internet, setting up a small network, and troubleshooting

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What to do when you can't connect to the Internet

Also, run the Airport Utility app which is located inside the Utilities folder.

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If using a  Linksys router, contact LinkSys Customer Support and/or post in their forums.

If using Apple's Airport, please re-post over in one of the AirPort Forums.