If you took your secondary out I'd guess that is the problem, its out of alignment. It's a little harder to collimate without a proper tool, but if you have an old film canister it should do the job. See
here and
here for details.
You can get a cheshire from Andrews for just $29, its basic but it works and its cheap! For a quick/light read on collimating (and general telescope information) I highly recommend the Orion XT6/8 manual. It can be downloaded from
here.