My Sony Ericsson K850i

Question

Why does my K850i restart?. There are times wherein Im using the media, and suddenly it just turned off then I had to turn the power switch on. Is it because of too much applications?.. Although It's just a new one, so I haven't added any applications yet and I've only added a few songs. I bought it in Macau so its probably made in China. My memory card is a 2gb micro sd. Hope you can help me with this, it's really bugging me. Thanks!!