You should always try a soft reset first. If it doesn't solve your problem you can try a hard reset. To perform a soft reset on a Treo 700w or 700wx:
1. Disconnect phone from charger and turn off the wireless mode by pressing and holding the Power/End key.
2. Turn the screen off and wait a few seconds.
3. Remove the battery for a second or two, then put it back in.

For the Treo 750:
1. Disconnect phone from charger and turn off the wireless mode by pressing and holding the Power/End key.
2. Turn the screen off and wait a few seconds.
3. Open the Mini SD card slot and locate the Reset button.
4. Use the stylus to press the Reset button.

Performing a hard reset will erase contact information and any third party software on the phone. Data can be restored after the reset by syncing. To perform a hard reset:
1. Disconnect the phone from its charger.
2. Open the battery door but do not remove the battery yet.
3. Press and hold the Power/End button.
4. While still holding the Power/End button remove the battery for about a second, then replace it while still holding down the P/E button.
5. You should see a message asking "Erase all data?" At this point you can release the P/E button and press Up to confirm the hard reset.