I simply can't see any sponsored listings when I serch for anything on Yahoo! Only organic results are displayed in my browsers (IE6 and FF). It's not a new phenomena, I could never see paid ads on Yahoo! at least for a year. However I can see the sponsored results when I do the same search on Altavista or ATW.
What causes it and how can I change it in order to see sponsored results in Y!?
Sounds like it could be spyware- a good place to start, at least. Scan your computer with several products. SpywareCatcher (free version) does a good job finding tons of stuff that adaware and spybot can't catch or remove.