The fact that you get 0 colonies with the pUC18 control and new cells tells me the issue is likely the transformation equipment not the cells or the plasmid or your technique. Something must be broken/changed to have no success.

Are you using chemicompetent or electrocompetent cells?

If chemicompetent, make sure the heat block or water bath temperatures are EXACTLY correct. The time and temperature is essential.

If electrocompetent, see if you can borrow someone else's machine. And make sure the cuvettes are the right type.

Good luck!

I agree with Katie A S Burnette that perhaps some more specific details about your cells and procedure would be helpful to diagnose the issue. Also it seems that everything at least worked once before so that's good.

Just to be sure I would recommend that you use a "high-efficiency" strain of E. Coli for this type of transformation. I have been using NEB #C2987 with much success.

If you are not even getting transformation of pUC18 control, is it possible that all your competent cell stocks in the freezer are compromised? Were they all in one box? Did the freezer fail?

We checked heats with thermometer every step. Maybe we can try electroporation method, thank you.

On the other hand, we thought maybe out component cells is dead, but we streaked them on the agar plate without amp and they growed. However, we can try another plasmid stock. Thanks for answer. :)