Hi all, I am new to this site and am building a new PC for my son for Xmas. This is the spec. Mobo= Gigabyte GA-P35-DS3 s775 ATX CPU: P4-775. CPU= Pentium core 2 Quad Q6600 2.4GHZ. RAM= 2 x Kingston 667mhz DDR2 DIMM . Graphics card= XTF GF 8600GTS 256MB DDR3. Hard Drive= Caviar SE16 500gb SATA 300MB/Sint Sata/300 7200RPM. Power supply 550 watts. Software= Vista Ultimate 32 bit format. I built the system a couple of weeks ago and when I booted it up the processor fan started then stopped a couple of times, I checked everything over which seemed ok and tried again. Again it did the same but I let it run and it booted up. I installed the soft ware put on my virus protection and plugged in the internet lead this sparked momentarily on connection and then the pc went off. I then cold not get the Bios to boot up, the system started but no keyboard lights or monitor activity. I have tried the hard drive, the power supply, and the graphics card in another pc and they are fine. I thought it may be a mobo problem so I have replaced the mobo only to find that it is worse as now, on top of the original problems when holding the switch down on the case it no longer shuts down the pc I have checked the switch with an avo and it works fine. In desperation I have unplugged the PC and flashed the "Cmos" terminals to see if this would help. As I see it, it is either the processor, the RAM, or the bios that is at fault could anyone point me in the right direction please. Thanks for your time and effort in reading this long post but I wanted to present all the facts to give anyone interested the best chance of giving the correct advice. Merry Xmas Andy.