Thank you

I have got four dollars in my pocket.

Thank you.

Any medical test will sometimes fail to detect [a condition when it is present and indicate that there is one] when there [not "it"] is none.

Any medical test will sometimes fail to detect [a condition when it is present and indicate a condition is present] when it is not.

David Eason suggests these versions:
Any medical test will sometimes fail to detect [a condition when it is present, and any medical test will sometimes indicate a condition as present] when it is actually not.

OR

Any medical test will sometimes fail to detect [a condition when it is present; any medical test will sometimes indicate a condition as present] when it is actually not.

OR

Any medical test will sometimes fail to detect [a condition that is present, and any medical test will sometimes indicate a condition as present] that is actually not.

I love taking stabs at rewriting awkward sentences! I did it this way to emphasis the contradiction between the two situations. (That is why I added the actually, which normally I avoid like the plague.)

Thanks!

What kind of a word is "not?" ex: She is not going to remember this very well.

The word not is an adverb. It tells you in what way she is going to remember something -- not. It's technically not part of the verb, but it modifies the verb so closely that it feels as though it's part of the verb.