Lose internet connection both wired and wireless,within a few minutes

Hello All, We have a Dell in the office that suddenly will not stay connected to the internet, either wired or wirelessly. It connects for about 2 minutes, and the I get "page cannot be displayed" message. Wirelessly it shows as connected to wifi router, but again the access disappears after a couple of minutes. I have run multi-anti virus scans, Malware Bytes, AVG, Microsoft etc. I see...