[Q] Htc hd2 keeps shutting off and restarting topic

Hey can anyone help, I bought a Htc hd2!! But it keeps shutting off and restarting , there is no pattern to this problem, it could do it before I put my sim pin in, or it could do it mid phone call or even after an hours use.... I can't figure it out.... I use a micro sad card in it, as I need to run the programme for work, it's running windows software....
Thanks gareth