I have a Hamption Bay ceiling fan that turns slow on all speeds.

Are you controlling it from a 3 speed wall switch?
If so then I suspect you have the fan motor pull chain switch set to low speed. The fan motor should be set to high speed with the pull chain and left alone, then and only then will the wall switch have total control over the variable speeds. Set you wall switch to high speed and try pulling the fan pull chain, until the fan speeds up. Once set leave the pull chain alone and the wall switch will now be the master control for the fan from off to high...
Bill

If the pull chains were not your problem try pressing the high speed button and hold it down for about 10 seconds

Is it a remote fan?

If not, it's the capacitor:

Ceiling fan capactors - troubleshooting and resources - Ceiling Fans N More (http://www.ceiling-fans-n-more.com/ceiling-fan-capacitors.php)