How are you determining activity? Did you oxygenate your wort when you poured it in or after it sat for a bit?
I would make sure your fermenter is sealed up. Most of the time, slow activity is due to the yeast doing aerobic activity and multiplying. Depending upon the date of the yeast packet and the storage conditions, your number of active cells may be on the low side and it will take them some time budding up new cells to start vigorous fermentation activity. I would give it another 24 hours to see if it develops a krausen and takes off. If you are unsure, give it another day and then take a sample for a gravity reading.
Let us know how it comes out!