Sudden shutdown problem with my Sony Vaio Z Series

Hi,
Recently I bought Sony Vaio Z Series as I love all Sony products a lot and Windows 7. But the main problem is that it is suddenly shutting down without giving any warning message. Sometimes it is shutting down after 20-30 minutes and sometimes taking more than 30 minutes. I tried to fix this problem like without using battery, plugging it to adapter. But no use. Today when I opened it, booting took less time, but after that it was suddenly shut down. Afterwards, I reformatted my computer, but again same issue. Can someone assist me ?
Thanks!
