It sounds like it is not getting enough light. Repotting once per year after blooms have dropped is a good thing. Use a high quality bark mix for orchids or high quality sphagnum moss. If the flower spike dried out you did exactly the right thing by removing it. So try more light without direct sun and be sure to water only if the mix is dry. No wet feet for most orchids. Good luck
Dendrobium species live as epiphytes and lithophytes in New Guinea, Southern China, Thailand, Japan, Australia, New Zealand, Tahiti and more. As a result, it’s hard to generalize how to care for these types of orchids. Some of them require cool nights of 50 to 59°F (10 to 15°C) while some of them require warm temperatures in the 80s°F (27°C). That’s why it’s so important to understand their natural environment so that you can make them happy. Learn more about Dendrobium orchids.
Do a finger test. This is the best way to determine whether an orchid needs more water. Stick your pinky finger into the potting mix, taking care not to disturb the orchid's roots. If you don't feel any moisture, or you feel just a little, it's time to water the orchid. If you feel moist potting mix right away, give it more time. When in doubt, you should wait an extra day.
Most orchids are not heavy feeders. Many orchids bloom year after year with no fertilizer at all. During active growth, when new leaves are being produced, you may fertilize every other time you water at half the strength recommended on the fertilizer package. However, it's important to deliver water without fertilizer at least once a month to flush excess fertilizer salts from the bark mix and avoid fertilizer burn to the roots.
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