Hi I have a cordless hammer drill with a problem!!?

Hi I have a cordless hammer drill called PRO. Recently its kinda lost its power. I mean it spins fast but on full torque settings for e.g. when i hold the rotating bit it just stops and makes a noise as in its still trying to spin it. Before it was impossible to hold and stop it especially on high torque settings. It would burn my hand by the friction. Whats the problem?