Q: iMac network status failure

I have airport and a router for wireless connection to my iMac, I've been using it for years and have NEVER had connection problems until just recently over the last few months, and it seems to be intermittent, it'll work for a few weeks then it wont work for more than a few minutes at a time, I also noticed it corresponds to apple updates...It keeps saying one or all of the following, "ISP failed" "Internet failed" "Server failed" when I use network diagnosic to reconnect, I'm able to stay connected for a short period. Can anyone tell me what to do?