cant open inbox msgs for yahoo.email acc

i’m running an internet cafe which uses ICS (Xp Windows) for internet connection. The problem is my other clients can open their email box ( primary Yahoo and Hotmail Accounts)but cannot access their inbox to retreive their messages (a cannot be diplay page appears). I’m losing a lot of clienttelle due to this PROBLEM . Please help me What can i do to fix this problem once and for all .