first of all we need to play Name That Orchid. go here
Orchid Photo Identification Guide
and see if you see anything similar.
second, is it just the flowers that are wilting or the whole plant? if it's just the flowers, don't worry; you don't know how long it was in bloom before you got it--it just may be finishing blooming. if it's the whole plant, it may be one of two things: not enough water, or too much water. or it could be other things.
helpful, ain't it?
tell us a few more things--what kind of pot, how big, what kind of stuff does it look like it's potted in, what kind of conditions do you have it in (facing which direction? window or artificial light? humidity? no humidity?) and we can take some more shots at what the problem may be.
can you post a pic of the plant?