If you live in a dry climate, you may need to install a humidifier. Then, install a fan to improve circulation because stagnant, moist air will lead to disease.
Orchid leaves will turn yellow if they experience magnesium deficiency, so if you're using a fertilizer that is too low on magnesium, you might be accidentally starving your plant.
Orchids can seem like they are dying when they're just experiencing a period of dormancy that can last up to nine months, so try not to fuss over them too much.