Sonnyma,
The link above is for USCIS Online case status system. However don't
be surprised if your case does not show up in the system. There seems
to be no rhyme or reason as to why someone's case shows up in
the system and why others don't.
BTW, the case status information which you get online at this
site is identical to the information provided by the automated
telephone system of the National Customer Service Center at 1-800-375-5283
But both are pretty much useless in providing any accurate/updated info
specific to individual case. All you get is some generic blurb such as
"this type of app is taking 365 days to process" etc.
If your case infact does show up in the online system, then you can sign-up
to get updates via email. Also from the feedback of others, it seems that
when the case disappears from the system at a later stage, more often
that not it means that you can expect your interview letter within few weeks.