Problems with my cell phone Sony Ericsson W300i?

This is the thing, i got that cellphone from my dad. its a year old but its in pristine order. after i checked it was alright i decided to download a few songs into it, only a few to see if it was working.

It was. so i then decided to download some ringtones and stuff. when i was finished i unplugged it from my pc the way it should be unplugged. the same way i unplugged it before when i first dowloaded the few songs i mention. but the darn thing wont turn on now. whenever i try to turn it on, i get a white screen that turns black and then white and then black and then white again and so on.

I used another phone to call mine and i dont get a "the phone is off" kind of message. instead it keeps ringing as if the cell phone were ringing.