Step 1. Turn off your MyTouch 3G Slide. If it won’t turn off, take the battery out and put it back in.
Step 2. Press and hold the Volume Down button while holding the power button to power back on your MyTouch.
Step 3. A menu will come up, use the volume up and down key to scroll to Clear Storage.
Step 4. Press and release the Power button to select Clear Storage
Step 5. Confirm your selection by pressing the Volume Up key for yes, or the Volume Down key for no.
Once you select yes it will complete the process and restart the phone. All data will be erased and your phone will be set back to its factory settings.