My w880i doesn't turn on

Question

i have a SE w880i it was working fine but then i was sending a song then it got jammed but after that i removed the battery and tried to on it it didn't work so i took the battery out for half an hour later i put it back it but now its been 2days and still my phone is not working i tried every thing i showed it in shop most of them said that the software needs to be flashed but i have bought my phone from 02 so i still have a guarantee because i bought it on pay monthly. so what should i do?