sprchng has some good advice!
Every once in a while my xmitter powers up but the headset acts up. When this happens i keep playing with the headset on/off/volume control. That power up control is sometimes tricky. Never had a time where neither unit ultimately refused to power up or link up. Also keep in mind that the xmitter times out shutting itself off if there's no link up with the headset. I don't know the exact timeout. Not sure if the headset wil timeout when the xmitter is powered off.
Also,
could be the mini-USB plug wasn't plugged into the headset properly. Those small USB plugs are delicate, don't force them.
Make sure when charging, both the xmitter and headset are showing red LEDs. The red will disappear and turn green when both are fully charged.
Note, the headset takes longer than the xmitter to charge up (typically 2-3 hrs. depending on how discharged the batteries are).
If the headset LED IS red during charging then turns green indicating a full charge and still won't power up, or it stays red forever, then in all probablility you're looking at a defective headset.