ohhh thats quit difficult!
in this case you have 2 options:
first: you wipe the dalvic cache
second: install an sbf file using rsd lite
the first option you will try as follow:
turn off the mobile
press the on button and the x button at the same time. when the motorola logo appears release the on button. you will see a little android robot..release the x button an push the on button once..you will see a menue..use the dpad to go to wipe data/factory reset and press enter if this happened you have to chose reboot system now!
i hope this will help