my home pageWhy do i have to make yahoo my home page every time I turn on my computer?

I signed up to make yahoo my home page. when I shut down my computer the next time I turn on my computer its on bing (which I don't like or want) I have to go back and remake yahoo my home page. I mean this is every time I use my computer
For any browser and any web page:
1. Navigate to the page you wish to use. If it is a mail page, do NOT sign in.
2. Go to Tools, then Internet Options (IE) or Options (FF). In Chrommy home pagee, it's the gear wrench, not Tools. For IE 9, Firefox 4 to 7, and Chrome, open the menu bar by right-clicking near the address bar (or click Alt or Alt & V) to see the Tools options.
3. Select the first tab or section (Main or General).
4. Select the option 'Use Current' page. (In Firefox, you can also 'Use Bookmark'.)
- OR drag the icon to the Home button (looks like a house) and drop it there.
- OR type in the URmy home pageL address completely -
5. Confirm.

(Some web pages have a message 'Set this as my Home Page link.)
(Ribbit)
Very simple. At the top , click on tools, then after click internet option, then click on home page block. Type the site name www.yahoo.com and ok.
Go to explorer Tools menu , Home Page, Type Yahoo.com and click use default and ok button try it.