My yahoo 7.0 don't work?

One night while chatting on yahoo, i suddenly realized i could not see IMs, i could not see what others were typing to me, however i could send IMs. I could hear persons on the mic and see names in the rooms but not conversations. I logged off and tried uninstalling yahoo and reinstalling still to no avail. I still have this problem after several days and more reinstallations. What should i do?