Have you looked under [VIEW] --> Toolbars? I assume the Startnow toolbar will be listed, and you can just uncheck it.
I think there is also a way to actually delete it, maybe under [Tools] --> Add-ons.
You can change the default search engine by clicking on the faint little downarrow just to the right of the search engine's icon at the left of the search box. The Manage search engines... option will let you delete unwanted ones.
The culprit may or may not be Microsoft. My copy of Firefox got corrupted in a similar way when I downloaded and installed a free utility from CNET, which I assumed was a reliable source.
Try to make a living, not a killing. -- Utah Phillips
Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
Law of Logical Argument - Anything is possible if you don't know what you are talking about.
If at first you don't succeed, try, try, again. Then give up. There's no point in being a damn fool about it. -- W.C. Fields