i have purchased one coil of 0.5sq.mm wire from the shop and without disturbing it, i connected one end to the 230V AC supply and other end to my SMPS ( whose output is 5V DC).

This is getting ridiculous, There is no way you are going to solve this by trying one or two "easy" means. Go through the noise entry in the FAQ and implement ALL measures, then come back and report.

You, as stated before, may succeed in one place to have it working for now by some means or other, but that is not a solution, the noise environment may change tomorrow.

Erik