There are a few different reasons why an orchid might not be blooming. The most common reason is that it doesn't have the right light level, so make sure that you check that first. You can look at the color of the leaves. Leaves should be medium-green. If they are a dark, lush green,the plant is likely not getting enough light. If that isn't it, there are a few more things to consider.  The orchid might simply be too young. Plants have to be mature enough to bloom and then only during their natural cycle. Your orchid might be overpotted. For best results with orchids, you'll need to make sure that they are tight in their pots. Pots that are too big for the root mass put the orchid in danger of not growing or blooming. Another problem could be that you're using the wrong fertilizer. There could be too much nitrogen, which suppresses blooming. You want a nitrogen phosphorus potassium (or NPK) value of 10:10:10 in your fertilizer. If you're dealing with limp leaves you will want to unpot the orchid and check the root system. If the roots are mushy then a significant root loss has occurred and there are several likely culprits.  Overwatering can do this. You can safely water an orchid about once a week, depending on the type and only as long as they are healthy and potted properly. Check the mix to see if it is drying out properly before you re-water. The pot is too large. This can also cause problems with your orchid's roots, because they are expending too much energy trying to maintain their root system rather than caring for leaves and new flowers. Potting mix has degraded. Potting mixes are only good for a certain amount of time before they need to be replaced. Make sure yours hasn't gone past its deadline. While pests are less likely in an indoors orchid, you can still get them in potting mixes and just out of nowhere. Make sure you know how to deal with these nuisances so you can keep your orchid alive and healthy.  Aphids target bloom spikes and buds so if you see holes in these areas you might have...

TL;DR in Vietnamese:
Xử lý lan không ra hoa. Chăm sóc lan khi lá héo rũ. Xử lý sâu bọ.