really really slow..and sometime it freezes

[furiousgtz]

yesterday my phone start acting wired..i try to open I.E and it open and then freeze..same thing happen to all my other program.. i restart the phone couple of time but still same proble.. then i had to sync all my date to my pc and so clear data to factory dafault now it works fine
does anyone know why this happen? or how to avoid in future.