I am experiencing the same problem.
When I sign in, i get the message
Temporary problem accessing your inbox.
When I click on the options link, I get another message
Temporary problem accessing your account.

It has been two days and it is all the same.I tried on many computers.
Please help me as I very very important mails coming.

Mine is a yahoo.co.in address
So I guess I will have to get yahoo India customer service number.
Can anybody help?

How long will the problem persist?