Use the free version of this anti-spyware tool: http://www.superantispyware.com/superantispywarefreevspro.html
If that doesn't help then download Hijackthis and post its log on one of the following forums for expert free help:
Do not post the log here, we can't help!
Post the logs at a specialist Forum:
WHAT THE TECH FORUM (Formerly Tom Coyote)
Be sure to read all the sticky announcements/instructions at the top of each malware forum!
I just encountered the same problem while accessing Yahoo mail. A screen came up with Dell at the top, and Google on the screen and a message about Yield Manager. It said to run Hijackthis because my mail had been taken over by malware. Since I wasn't sure where this advice to run HijackThis was coming from, I had to come here to verify that was the proper thing to do. I just ran SuperAntiSpyware a few hours before this happened. While I was busy doing other things, I decided to run Malbytes, but it didn't pick up anything, although I just rebooted after running that and was able to access Yahoo mail without a problem. I think I will run SuperAntiSpyware (an excellent, helpful tool) again and then HijackThis, I am so thankful for this site because when an instruction comes up on your computer, like run HijackThis and you don't know where it came from, you are quite leery. There are so many programs that want to run scans, then tell you that you have like hundreds of problems that can only be fixed by purchasing their product. THANK YOU SOOOO MUCH FOR BEING HERE AND ALL THE HELP YOU HAVE BEEN TO ME. THIS IS A TRUSTED SITE!!!!!!!!!!!!
This is such an old thread I suggest you start a new discussion if the problem continues here: http://community.mcafee.com/community/security/malware_discussion/consumer