do you have a housekeeping gene primer set that can be amplified to show that you have good quality cDna.

Can you borrow a dna sample that has worked for another researcher to test your primer/pcr conditions.

Does your tissue normally express vdr

Are you sure that the RT part of the process is working well and that all the RT reagents are within date

When you say the pcr did not work do you mean there was absolutely no reaction or that there was primer dimer or the wrong size band produced

As Paul said: begin with ruling out what could be the problem by conducting positive controls

- does the polymerase work (I had once two bad batches in a row)?

- does the reaction work (if you see a low-size white smear on the the gel the reaction basically was able to piece together something double-stranded?

- play with the annealing temperature: go down a couple of degrees

- find a way to make sure that your samples are ok. Are you sure, they contain DNA?

All this will get you closer by excluding some factors.

Good luck!

In addition to answers given by Paul and Dominik,

1. Do you know the annealing temperature for the primer pairs? If no, then use this link to calculate the appropriate temperature

https://www.thermofisher.com/in/en/home/brands/thermo-scientific/molecular-biology/molecular-biology-learning-center/molecular-biology-resource-library/thermo-scientific-web-tools/tm-calculator.html

2. Plan a gradient PCR with a known DNA sample (don't forget to include a housekeeping gene such as GAPDH or beta ACTIN)

Overall, my suggestion is don't jump into changing MgCl2 concentration before checking the proper annealing temperature, primer concentration, and most importantly your sample integrity. Make sure to run a 1% Agarose gel for DNA and 1% Bleach agarose or MOPS agarose gel for RNA to check the quality of your nucleic acids.