Inspiron 1525, motherboard?

I had posted previously about where to get a keyboard, since I thought that was the problem: http://en.community.dell.com/support-forums/laptop/f/3518/t/19589084.aspx I marked that post as "answered", so I assume I have to start a new thread. I ordered new keyboard, but when replacement keyboard arrived, the same keys don't work on it. Bottom row of keys (Z,X,etc), space bar, Enter key don't work. Left shift and ctrl work, but not right shift and ctrl. Up arrow works but not the other arrow keys. USB keyboard works fine, all ok with it. Could there possibly be some problem other than motherboard? I've reseated the ribbon cable onto the motherboard socket many times, and I don't think it would work at all if that was the problem? Can anyone think of anything else to try? If motherboard is likely the problem, which model? I've gone to the configuration site at Dell, and while it lists many part numbers, the motherboard part is not listed. At Parts-People.com, they list two models, PP385 and PT113. I see the same models listed on Ebay. Is there any way to tell which I need, short of disassembling & removing motherboard? I know I would have to do that when replacing, but don't want to do it twice. Thanks, Steve