Explanation:
You can do two controls:
1) Check if the cells are viable by plating the transformed E.coli on LB medium with no antibiotics. If the cells are alive, a lawn will be seen, as there is no selection pressure. If the cells are dead, no colonies will be seen.
2) Check if the cells are competent by transforming them with a control plasmid. This is another plasmid, either commercial or already used in the lab, that contains the gene for resistance to kanamycin, and is known to work. If this positive control is used to transform the cells and still no growth is seen in the LB plates, then the E.coli are probably not competent.