Cannot access email


New Email
After a Dell technician took manual control of my computer, I can no longer open my Yahoo email. I have an Indiana University account, and I can open that email, just not The modem and the router and everything is connected and I can open any internet browser. I have been online with an AT&T tech. and also have been on the phone with two tech. from AT&T and still no luck. Since everything is connected and all defaults have been checked, what could be the problem?