What does your positive control look like? Can you amplify any target genes from that particular RNA samples (e.g. actin)?

Did you try running out an aliquot of the RNA on an agarose gel to look at the quality of the RNA? Or use a spectrophotometer to look at the purification?

Katie A S Burnette Thx a lot for your answer.

No but I will definitely try it.

I just read it with nanodrop. ODs ranges were about 100-500, and there were also a little pr and phenol contamination (I exctracted RNA using manual trizol method).

Katie A S Burnette Ct of GAPDH gene in few samples were 35.

At Ct value that high means you have minimal amplification.

Phenol will inhibit your PCR. Better start over.