Help with RT-PCR!!! What's wrong with my primers?

[Miao]

Hi,

I use invitrogen one-step RT-PCR kit. None of my 5 pairs of primers
give me any visible band! I did a lot of control, so I am sure that
the kit still works, my RNA template is good also.

I even tried those primers to amplity from plasmid (containing my
gene's cDNA), but none of them worked!

All of them look OK, annealing temperature not very different,
reasonable GC content, length 20-25 nucleotides.

Could somebody help me? I am so dissapointed!

Miao