Re: XPS 420 CPU Switched Off by Itself.
8 GB (4 x 2 GB) Kingston DDR2 800 MHz SDRAM Memory
Leadtek WinFast GTX460 1GB OC, 725 MHz Core, 3600 MHz Memory
"I can get into the BIOS, but shortly after that, the computer switched off by itself"
what i would do is; only re-install the factory RAM and remove the GTX460 and boot into the BIOS and see what happens, it is rare for bad PSU