Site-directed mutagenesis (repeat oligo insert) - Strange mutagenesis reults! (Dec/22/2009 )

Hi..I did site directed mutagenesis using Quick Change Stratagene Kit in but there was no amplification. My primers had high GC content about 74% (Tm=83) so there might be more chances of self annealing. I tried using DMSO from 1 to 5% but still there was no amplification. Any ideas for troubleshooting this problem???...