First of all check your DNA with normal PCR, that gives you an idea about the DNA  and primer quality.

Secondly just check your PCR reaction initial denaturation temperature i.e, 50 degree for 2 min generally it is 94 or 95 for 4 or 5 min.

Do you know what bp should be the product?. When you use sybr green, did you use real-time pcr machine? The protocol you used is two-step cycling protocol. Try to use more common three-step protocol: 50°C 2min; 95°C 10min; and 40cycles - 95°C 15s, 60°C 30s, 72°C 30s and also do the disociation curve to analyse the product i.e. if there are non specific products or primer dimers.

hi Fernanda Trindade da Rosa, In your question you said that no visible bands are present except marker. Are you sure that even primers are also not visible?? If even primers also not visible then mostly your test set up might be contaminated with nucleases. Try to use new or sterilized tubes, tips which are the main sources for nucleases. Also once check the genomic DNA purity and also run a gel to check whether it is degraded or in good condition.

    If above description is not the condition, then explanation of others will be helpful to you. 

I would use Boris's cycle and different amounts of dna ( 3ul tells us nothing about the amount of dna used) . If your dna contains inhibitors then less is needed or if it is mainly rna then possibly more is needed so titrate the dna. Also use another set of primers if possible just to ensure that your dna works in pcr and if someone else in the lab has the correct dna borrow some. also check the sequence of your primers to ensure that they exactly match the dna sequence you are amplifying especially at the 3' ends of each primer. A mismatched base near the 3' end of a primer will stop extension and pcr from working