It really depends on the conditions you have the plant in. Hibiscus need warmth, not too dry of air, and sunlight. Lots and lots of sunlight! They will survive just fine under low light conditions, but they THRIVE with lots of sun. Being root-bound will also slow their vigor and reduce their flowering, and they do get root-bound easily because most hibiscus generate lots of rootage. Depending on where you got your hibiscus from it is most likely root-bound. If you got it from a greenhouse or nursery, I would bet, for sure, you need to repot. I would bet that if you repot and put the plant in a sunny window you'll get flowers in no time. Do try to keep it from cold drafts while it's flowering because you'll get buds dropping off before they open (that's extremely frustrating).
Good luck!