Internet connection problem

My internet service provider recently ran fiber to my office. They had a few issues with it not working, but it has been working for a few weeks now. Tuesday afternoon my internet was down. I contact the ISP and they were having problems in my area, so we checked Wednesday morning and IE or Chrome would come up with my home page but when I would try to go to a website it would either take about a minute or not work at all. We called the ISP and they said it looked good to them. After some troubleshooting. I pugged the cat5e cable from the ISP into one of the computers and it worked great. I did a speed test and got 19.42 Mbps down and 4.82 up. I plugged the cable into my Linksys E1200 router and all 4 computers slowed to a stand still. I tried a speed test but I couldn’t get it to run. I tried to ping yahoo.com and I would get 1 time out and then a reply and then the rest time out, so I replaced the router with a Linksys EA2700 and now I am getting the same thing. I did finally get a website up after 45 seconds one time. All 4 computers do the same thing.
I have reset the router back to the factory setting and nothing helps. It works great if I plug one computer into it but when I plug the cable in the router I am toast. I even tried bringing a router that I had at home that was working fine and it did the same thing.
I have tried 4 routers. Three of them were Linksys and the 4th is a netgear. It kind of worked for a half a day. I tried a different Linksys and it slowed to a stop.
I can’t figure out what I am missing.
Thanks, for any help