Samsung Galaxy S i897 not detected by PC

I have read every forum and every "help" site on Samsung's website and all over the internet. Nothing has worked. I bought an unlocked Galaxy S i897 on ebay, originally an AT&T phone but I'm using it on T-mobile. Is this potentially the problem? I've tried 2 different cords, only charges, never recognized in any Kies version and never recognized by PC like step 3 on this page says it should. http://www.samsung.com/us/support/SupportOwnersFAQPopup.do?faq_id=FAQ00045584&fm_seq=46246 Extremely frustrated at this point. I don't think calling t-mobile can help because the phone was AT&T. Samsung probably wouldn't help either because I bought it on ebay. Unless you think they would, then let me know. I just want to add music and transfer files back and forth, backup contacts, etc., and most importantly update my firmware (currently has Froyo).