During performance of one-step RT-PCR reaction, however the reference gene is expressed, the target gene not determined by 7500 fast apparatus, is that because the extraction purity is not enough or the issue related to primers design only.
If the reference gene is amplifying well but your GOI is not, it is probably a primer issue. That being said, you need good quality RNA for qPCR, particularly if you do a one step qPCR. Use a RNA kit to isolate your RNA. Otherwise inhibitors will affect the efficiency of cDNA synthesis and produce a lot of variability between samples.
This site might help: http://www.lifetechnologies.com/au/en/home/life-science/pcr/real-time-pcr/qpcr-education/real-time-pcr-troubleshooting-tool/gene-expression-quantitation-troubleshooting.html
Both the RNA purity and intergrity measured by RIN (RNA intergrity number) affect the final outcome. If feasible check the RIN its recommended it should be above 7 and 10 being the best.