Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
What were the faint black marks on the paper like? if they were lengthwise and running along the length of the paper, that's one thing (and usually a problem in the inking system, or with spilled ink inside the printer); If they were just a touch here and there, that's probably paper feed rollers that are a bit dirty and need cleaning.
Where does the paper jam? the place in the printer that it happens, can be quite significant in the curing of the problem. The problem is in fact right about where the leading edge of the paper stops, almost always.
Check that area for dirt, fluff, paper scraps, etc., and clean out any that are found.
Check that you do not have a different size than "Letter" or 8.5 x 11 inch paper selected in either your software or your printer driver settings. That can cause paper jams that are spurious simply because a different size of paper is expected, but 'Letter' is what is sensed by the printer instead... which makes it think that longer or shorter paper has gotten folded or jammed otherwise, and stops it from working on that assumption.
Also try shutting the printer Off for 1 hour or more. Sometimes these errors are spurious or 'persistent' but when the printer's memory is quite cleared by a rest-reset, the error goes away.
Let me know how it goes, and more details as needed. Thanks.