I can't help you since I never encountered this problem (I always open links in a new tab), but I wonder why you prefer to open a new instance of the browser instead of using tabs?

>I usually have several IE instances opened. I think I found that at some point IE7 simply closes itself (all the instances).
>
>Say, I was researching the problem and tried to open a google link and all instances of IE simply closed.
>
>Same problem happened yesterday as well when I tried to open one extra link.
>
>Did you observe something like this?