OK, so you have an anti-virus. that means it is REALLY unlikely that you have a nasty changing settings for you.
First off assuming you are using internet explorer as that is the default browser in windows 7 you need to:
click the cog button (top right under the "X")
click internet options
select the programs tab
click "manage addons"
on the left hand side click "search providers"
Select google in the list
Click the "set as default" button (close to the bottom right)
Tick both boxes in the bottom left. the top of the two prevents future changes to your search provider and the bottom one makes it search from the address bar using google.
now on to your Hotmail problem, there are a couple of things to try depending on what is happening.
If you get to the login page but your password does not work
The first thing to try is typing your email address and password in to notepad (start (the blue round button bottom left with a picture of a flag on it), all programs, accessories, notepad). This doesn't do anything other than let you check that your keyboard is putting in the correct characters. Various countries have the letters in the same place as is but the characters $£#@ etc are on different keys.
If the wrong characters appear then either you have a sticky key or the region is set wrong. a sticky key means new keyboard time as they are less than £10 and not worth taking apart to clean. changing the region is easy enough and if that is what's wrong I can post instructions on that too.
If you are getting a page cannot be displayed error
Just checking that in the address bar you are typing
http://outlook.com or
http://www.outlook.com rather than just outlook. It is entirely possible that Ask search isn't working correctly so you need to type the full web address in rather than just the name. if you have followed the instructions above it will fix that.
When you visit outlook.com does the address bar turn green even if you get an error?