A Soft Reset stops all active (or open) programs and "reboots" the handheld. When the Treo powers back up, you'll start with all programs closed and the unit will be ready to use. The soft reset is intended to reset the Treo if it is malfunctioning or has become bogged down.
The Palm Treo 750 can be soft reset by quickly pressing and releasing the tiny red button beneath the miniSD memory card door:
A Hard Reset wipes the internal memory and returns the Treo to its factory specs, in effect returning the Treo 750 to the state it was in when you purchased it. All data entered, preferences set or software installed on the Treo after purchase will be lost after a hard reset and will have to transferred or reinstalled via ActiveSync / Windows Mobile Device Center.
The Palm Treo 750 can be hard reset by pressing and holding the power button (seen left) while at the same time pressing and holding reset button beneath the miniSD memory card door. Press and hold the two buttons until the screen completely fades. When the screen returns, you'll be given the option to "Erase all data." Select Yes to complete the hard reset.
The Treo will now be as it was when it left the factory and you can start fresh. You may have to perform a soft reset after the hard reset to get the unit to power on.