I think knowing what type they were would definitely help.
Overwatering might be the problem, how much and how often are you watering? Also some orchids are deciduous.
If it's any consolation, the first orchid I ever had lost all it's leaves and I assumed it was dead, but later read somewhere that it might have just been resting..I shall never know! I think if an orchid is resting you have to leave it dry until it starts to show signs of life again, and then you can start watering it again, but I'm no expert, I have very little luck getting my moth otchids to flower again, but my dendrobiums are great for flowering :-)
SP