Yes your guess may be is right.
Below is activity to remove any possibility of infection, but before give one try changing you Primary DNS to 188.8.131.52 and secondary DNS to 184.108.40.206
Might be DNS issue. Follow the link on how to change dns
Try accessing yahoo mail. If still doesnt works. You can try following
Before running winsockfix make sure you note down ip address and dns settings of your LAN Card. May refer to above link on where you can find ip and dns information
Run winsock fix
There might be malware, spyware, or adware infection on your webbrowser.
Best way to deal with such kind of issues is to boot in safe mode and clear all your temp and temporary files.
1) Open Internet Explorer and click on Tools
2) Click on Internet Options
3) On the General Tab, in the middle of the screen, click on Delete Files
4) You may also want to check the box "Delete all offline content"
5) Click on OK and wait for the hourglass icon to stop after it deletes the temporary internet files
6) You can now click on Delete Cookies and click OK to delete cookies that websites have placed on your hard drive
Also, try downloading and executing some of spyware and related kind of virus removal tools. Below are few such tools
Hijackthis, This tool is most effecting and also screw things up if not used properly. Remove only things which looks like going on browser and starting from http or some enteries with "no files" or "missing" keyword
Do not remove select or remove any entries starting with HKLM
and also make sure not to delete any entries which sounds like your antivirus, sound services, display services etc
refer to link for more help on Hijackthis ( I really love this tool )
Hope this help