internet blocked

imac is blocking internet wireless and wired connections, I was using yosemite on my computer when the internet was suddenly blocked, I have had my provider check on the service and all is good. I have a wireless network with a laptop and ipad running, when the imac block the internet, the wireless will not work on my other devices, when I turn-off wireless and unplug my cable to the mac then then devices will work. I have others tell me that the problem was in yosemite, so I backed up and wiped the HD clean and reloaded with Mountain Lion, and updated, after the update the problem came back, same thing as before. If anyone has had a problem like this PLEASE< I need help on this, this is the 10th day. just a note: I am not using ethernet and wireless together on the mac.

Your post wasn't clear...have you tried a direct Ethernet connection?

Why are you using ethernet and wi-fi on your iMac? Turn off the wi-fi and only use the wired connection (ethernet cable). That's how I have my iMac set up and I also have a MBP, 2 iPhones, and 2 iPads all on wi-fi. Everything works as it should with that set up.

Still not sure why your iMac would interfere with the wireless network in your home...

imac is blocking internet wireless and wired connections

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You didn't say what was connected by wired connections. Everything you described was WiFi. Hard to help when the problem is unclear.

I agree with member "MYmacROX". Why would you have your ethernet cable attached while using WiFi? And, when was the last time you reset your router? And while on that subject, how old is the router? I've seen the problem you described here before and it was usually a problem with the router. Your iMac can't "block" the internet for other devices.