which browser do you use? I'd suggest downloading firefox if you haven't and try it with that.. or use IE if you use firefox..

also it could be a cookies problem.. make sure your cookies are enabled cause yahoo doesn't work for me cause i disable cookies, so i have to use IE when i use yahoo..

umm.. those are the simple ways to solve the problem.. they also may be real obvious and you may have tried them already..

worse comes to worse maybe re-install your browser.. seems like a simple browser problem and you can fix anything with re-installing.