I'm working with Douglas fir microsatellites - I have six loci that I optimized previously for primer conc, MgCl2, temp and cycle number. I amplified about 300 samples without trouble, then took a month or so to do some genotyping. Since I've started trying to run the reaction again, I have been getting a ton of background amplification sometimes with my primers, and now recently no amplification. I have ordered new primers, and replaced buffers and dNTP's (though I haven't ordered NEW dNTP's). I've also checked these primers against DNA we've previously amplified and my current problem is showing up. Any suggestions?