Why does my Yahoo toolbar dissapear?

I have just bought a new gaming computer that has Windows 7 and IE 8. It came with Google Chrome and I installed regular Google toolbar and yahoo toolbar. The Google toolbar has stayed put but my Yahoo toolbar keeps disappearing when I close out IE. It does not show up under tools - toolbars so I cannot put a check-mark to make it appear. I look under manage add-ons and it has disappeared from there also. Why will it not stay put? How do I make it stay when I close out my IE 8? Google stays put. I have tried to disable Google and making Yahoo my default search but that didn't help. I checked to see if it was my anti-virus but it is not the reason my toolbar is disappearing. I keep having to reinstall the Yahoo toolbar every-time I closeout IE and it is getting very irritating so getting this corrected is a priority. Is it because Windows 7 hates Yahoo and doesn't want anything to do with it? Ot is it the personal controller thing? Any suggestions would be appreciated but please put instructions for a dummy as I am not a computer person. Thanks!