Certified GKH Gardening Expert
If they are in standard potting soil, or dirt, then this will be the issue. They are epiphytic and will live primarily on the bark of other trees. Soil will be too heavy, and remain wet. Orchids can not tolerate these conditions. Soil should only be used if it is directly specifically blended for orchids.
Too much light can also be problematic, as can too cool temperatures. There are many factors that can cause an orchid to suffer.
This article will help you to care for orchids: https://www.gardeningknowhow.com/ornamental/flowers/orchids/indoor-orchid-care.htm