What could my problem be?

[hi]

While I do maintain that I am somewhat tech-savvy, this problem has stumped me a bit. My desktop's symptoms:

1.Can't update Microsoft Security Essentials. It's saying there's a loss of internet connection. When I diagnose connection problems, however, I'm getting an opposite message, saying everything is a-okay.

2. I can only access sites like Facebook, Myspace, Twitter, etc. Everything else shows as a loss of connection.

3. Computer is somewhat sluggish, but it's quite old (6-years-old).

4. Upon downloading Google chrome, I get an error every time I try to open it.


5. I get re-directed in a new tab on Firefox when I Google search something. And the page is relevant to what I searched, but not exactly the link I clicked on...

I'll be buying a new modem soon, but what can I do for the time being?
Oops, forgot to mention I have MBAM and nothing comes up detected.
I cleared my cache and cookies already. I defragged about a week ago. I can't update MSE because of the loss of internet connection. But I'll try it in SM I guess.