Ok, without knowing more about your situation, let me try to walk you through what I can think of off the top of my head.
* Launch IE. In the menu, go to Tools / Internet Options / Security
Make sure the sites you wish to visit (yahoo.com, hotmail.com, etc) are listed under the "Trusted" zone. (Click the "Trusted" icon, then the "Sites" button. If they're not listed, click "Add".)
For Hotmail, you've got to add *.hotmail.com, *.msn.com, *.passport.com, *.passport.net, *.passport.org, and *.live.com to the Trusted zone or "Hotmail" won't ever load.
And as bad as it is, click the "Reset to Defaults" button on the Trusted zone security level. If you've got it (or it's been set) too strict, n0one of those sites will get a chance.
* If you're running a firewall program (such as Sygate), then make sure Hotmail, Yahoo, et al are in the "Trusted" or "Always Accept" list. You may have to tell it to allow IE to access those specific sites.
* Launch FireFox. If you've got the "No Script" extension, you can right click on the NS icon & select "Always Allow This Site". Otherwise, make sure FireFox is set to "Always accept cookies" and check "From originating server only".
* Reboot.
You should, hopefully, be able to access Hotmail & Yahoo.
(I was unable to access Hotmail for a week because my Firewall & FF extensions were killing it entirely. It took a week of troubleshooting FF before I realized that the Firewall was part of the issue, too. Now I can get back into Hotmail. *sigh*)
Hope That Helps! =)