| | Re: PCR Primers same as cDNA Primer?
Primers are different for cDNA - they are polyT or random primers whereas pcr primers are specific primers generated from your DNA template sequence.
Primer usage depends on your definition of primer types, and how you originally designed your primers. If the primers you use on your cDNA were designed to cover exon/intron boundaries, then those primers are not going to work right on genomic DNA because the introns are present. In that case you would need to design new primers. These will be very similar in that they'll be 20-ish-mers of DNA, but will have a different sequence.
Since all you're seeing is primer-dimers, I'm guessing this is the case. You could try messing around with the annealing temperature and MgCl2 concentration though if you think it should be working, and compare the sequences of the primers, cDNA, and genome to make sure they're all lining up and matching.