you should try to see if the supercoiled plasmid you are trying to clone gives colonies. maybe the antibiotic you use doesnt fit the marker on the vector. If the supercoiled vector does gives colonies, then there is a problem with your ligation reaction, either the reagents are not good or the sticky ends of your insert doesnt fit with those of the vector.

Well, This is a very common problem being faced during cloning experiments. 

The major reasons for  failures could be

1.competency efficiency of your cells. It should must give a lawn or approx 10^6 cells per ug of plasmid transformed. 

2.The improper double digestion of your insert and vector

3.The ratio of insert to vector taken during ligation(1:3 0r 1:5 or 1:8). Try to estimate the concentration through band intensity on agarose gel and not from the nano drop as it fails to reject the other nucleotides in your samples.

4.The last and most important factor is ligation buffer and the ligase enzyme. Make sure they are not too old. Frequent freeze and thaw of ligase buffer dgrades the ATP present in it. 

Good luck

Sounds like a reagent issue.

Gaurav is correct, lack of proper efficiency of competency cells is a common issue, competency cells loss efficiency fast if not treated properly (numerous freeze/thaws, left at room temp too long, etc.).  Another common source of error is the ligase has lost activity.  I would try a new batch of cells and a new aliquot of ligase and fresh ligase buffer.  

Additionally an extended digestion time of your vector is very important, you want to be certain that your vector has been properly cut by both enzymes.  It is sometimes impossible to detect (depending how close your cloning RE sites are to each other) whether you have a double cut or just a single cut.  If you are getting a single cut and then phosphates your vector the cloning reaction will not work.

Additionally don't phosphates your insert, I did this my mistake one time and surprise, surprise the cloning reaction didn't work ;).

Estimating correct insert-to-vector ratios helps but in my experience isn't a make-or-break type of situation.

good luck