Please help, I need help reviving my orchid

[mexitica]

Hi,
I am new to this board and to orchid growing as well. I love orchids and had tried growing them in the past with no success. I now have 2, that have been with me for over a year and looking good. One just lost it flowers and leafs look very nice.
I was recently at a super market and saw an orchid on sale, looked a bit limp but bought anyway. Well I have had it for about 3 weeks, I noticed when I purchased that it seemed dry so I watered with my fertilizer and water as I do my 2 others about every 15 days.
The leafs look leathery and dark brown almost burgundy color and limp. I started looking onlne and found this site, I took it out of the pot and immediatly felt the moldy smell that came out. The roots are dark brown, stringy and mushy. I cleaned everything and see that about one or two little stubs of firm roots are left. What can I do, please help.