Inge, welcome to participating here!
This is probably better discussed in the Orchid chats and Orchid care threads, but if I may - Inge, you don't mention the source of your Orchids. Especially in the beginning it is very important to buy good plants, hopefully of good size and being healthy, ready to take off in your possession. Buying from established reputable Orchid vendors is important.
Also, in general hybrids are easier to grow than species.
It may not what you did to an Orchid ( in your case the Ornithophora radicans) for it to decline, but you might simply had a poor plant to begin with. Or, your conditions are simply not a good match with the cultural requirements of the Orchid.