Could somebody tell me what is wrong with my plant?

Could it be the soil is kept too wet? How long have you had it,any history, any repotting..?

Hello and welcome! A number of things could have gone wrong, but if you could provide more information about the position (is it always where you have photographed it, or have you moved it from elsewhere). Are these blinds kept closed or open and which hours of the day. How often do you water her? Could be overwatering, as Sally suggested, but more info is needed.

As others have noted, we need more information to give a definitive diagnosis.The leaf symptoms seem to be more associated with too much direct sun and/or too little water.

The plant is about two months old. I re-potted it the same day it was purchased. It was previously placed several feet from the windows but about a month ago I placed it near the window/door as shown in the photo below. The room is very bright on a sunny day. The plant was growing nicely but in the last month, I noticed drying/yellowing leaves. I water plant one a week. Excess water is discarded and not left in plate. I mist leaves when they appear to be drying out. I fertilize every two weeks with fish emulsion fertilizer 5-1-1. I suspected the yellowing leaves had something to do with watering but I cannot tell if it is over water or under watering.

Thank you very much for listening.

I cannot tell the direction the window faces and whether the sun's rays fall directly on the leaves at some point during the day. If it does, then I think that is the problem.

As for watering, once a plant is repotted it makes it difficult to know when and how to water properly as watering depends on pot size, soil quality and how much the original rootball was disturbed during the repotted. I suggest that you stop fertilizing and if your tap water is hard, use distilled or filtered water instead.

@WillC, could it be a problem of overfertilizing, or unecessary fertilizing if I may put it another way? i think that the plants are supposed to get fertilized in spring till start of the summer months, when growth is due, not in winter? Thank you.
@Delight12, I have two Dieffenbachias, they need the light, but not direct sun, which dries the plant, so if sun gets on the leaves, move it further from the window. Leave it there, where it would be cooler and go from there, see how it reacts. I hope your plant recovers!

Faridat - Over fertilizing can be a problem, but I don't think that is the case here. The plant would probably have to be fertilized at 10 times the recommended rate to cause that much damage.

Thank you for your comments.

I have moved plant to a cooler location - well away from the window. I won't fertilize until Spring.
Do I cut off the yellow and dry leaves?

The discolored leaves will never get any better and will probably get worse. You can either remove them entirely or try to trim off just the discolored portions. Do whatever makes it look better in your eyes. Trimming leaves will not affect the health of the plant.