Computer no longer powers up

Hi everyone. I'm hoping someone here might have some intel with this problem.
I just purchased an entire system & built it this past weekend, the 27 & 28 Nov. These are all the components and periphials: SONY Black 1.44MB 3.5IN FLOPPY DRIVE
CREATIVE SOUND BLASTER AUDIGY 2 ZS 7.1 1394 24BIT OEM SOUND CARD
Samsung SyncMaster 793DF II Dynaflat 17IN SILVER-BLACK 1280X1024 .20MM(H) VGA CRT Monitor
BenQ Optical Wheel Mouse BLACK-SILVER PS/2
Logitech Office Pro Keyboard Black PS/2 W/ Multimedia Keys & Detachable Palm Rest OEM
BenQ DW1640 DVD +RW 16X8X16 -RW 16X6X16 Dual Layer +R 8X -R 4X Black IDE OEM Burner W/ SW
Seagate Barracuda 7200.8 200GB IDE ATA100 7200RPM 8MB 8MS Hard Drive 5 Year MFR Warranty
Kingston ValueRAM PC3200 512MB DDR400 CL3 184PIN DIMM Memory
ASRock P4VM8 MATX PM800 S478 DDR AGP 3PCI AMR SATA RAID VIDEO SOUND LAN MOTHERBOARD
Intel Celeron D 325 2.53GHZ S478 Prescott 533FSB 256KB Cache 90NM Processor Retail Box
LOGITECH X-530 5.1 SPEAKER SYSTEM Black 70W RMS 140W W/FDD2
Casedge TW-02 16IN mATX Mid Tower Case 2X5.25 2X3.5EXT 1X3.5 300W Black Matte Finish /W Air Duct

All went well Saturday and Sunday installing, etc. Everything was working fine and had OS installed (XP Pro) & working and shut computer down Saturday night. Started it back up on Sunday morning, got all hardware discs & programs installed, etc. Installed Norton Internet Security 2005 but removed it as I could not leave Norton Antivirus off, and installed Grisoft AVG. All working well. Started downloading updates from Microsoft. Re-booted everytime when asked and everything worked fine. Installed Everest Home Edition from Lavlys and printed a summary and it all showed OK Checked the Device Manager and it showed all was OK except for the USB2.0 driver not being installed so I installed it off the m/b disc (must have missed it the first time). Shut computer down Sunday night. Went to turn computer on Monday morning and all that would power up were the fans and enough power to light the led's and open DVD drive. No boot up of any kind on monitor; no CMOS, nothing. Re-checked all connections just in case, (the case was not even open any more, so I am not sure how anything would have come loose). Tried starting again but same thing happened. Tried restarting about 5 or 6 times with the same results then all of a sudden, the next time I tried restarting it, nothing... no power to anything. Tried changing power cords. Didn't help. Re-checked connections again and tried 2 more times. Nothing. The next time I tried it, I had power again but still same as initial problem. I even swapped ouy the power supply to a 350 watt but same thing. Took everything off m/b including processor and re-built. Same.
I tried again this morning. Completely re-built everything again with exception of pulling m/b out of case. Even tried to reset CMOS but no luck. I'mstarting to think either it's a faulty bios or cmos chip or the m/b is toast.
I'm kind of desperate as I'm building this for a cousin and it was working when he was here on Sunday to look at it. Please help if possible. Thank you.

It sounds like your guesses could be right.

You've rebuilt the PC, you've reset the CMOS and swapped out the power supply - So we know it has nothing to do with these things, providing everything was done correctly.

Hardware failure is looking very likely at the moment.

You may want to try tearing it down again, but only leave the absolutely basics connected. System board, CPU, video and memory... Then turn it on and see if it works. If it doesn't work, you can blame one of these components. If you have parts lying around, the best thing to do is swap them out systematically until you nail what the problem is.

If you don't have that luxury, then things are going to be pretty tough. You may want to return the items in question and buy new ones, but I know those restocking fees and online shopping policies can be tough.

Thanks

Thanks Rick. I swapped ram; no change. Pulled battery from m/b; no change. Left everything off m/b I could and didn't even hook up drives, just m/b with cpu & ram. Still the same. I'm still waiting for Tech Support from where I bought it all to reply. Unfortunately I don't have another m/b or cpu with the same socket size or I would have checked them out too. It's got to be either the m/b or cpu that's toast but I guess there's the off chance that it's the bios chip still, but I doubt it.
Just like to add to anyone who reads the forum that without support like this on these forums that a lot of people would be spending a lot of money when they could have fixed it themselves. So a sincerest thank you to all who contribute and I hope I can give help as well. Lloyd.