Two Computer Builds, Two Problems (Long & Detailed)

[DHC120]

Leave it to me to create twice the work for myself, as well as twice the problems..
I decided to "upgrade my system" (aka build a new computer) with the following parts:
ABIT KN8 MB, AMD Athlon64 X2 3800+ Dual Core Processor (with the AMD Heat Sink), an Antec 430 Watt TruePower 2.0 Power Supply, four One Gig Sticks of G.Skill Ram and an XFX GeForce 7300GS PCI-Ex16 Video Card.. and a neat black case to put it all in (4 5.25" & 2 3.5" External Bays and five 3.5" Internal Bays).
Given the the "parts" I'd have left over, I opted to "get a few more items" and build my son a "bigger/faster" computer, using my old case.. so I picked up the following:
ABIT AX8 MB, AMD Athlon64 3600+ Processor, Antec 350 Watt SmartPower 2.0 Power Supply, Four 256MB Sticks of RAM and after the parts arrived, realized there is no "VGA"card slot, only a PCI-Ex16 slot, so I spring for a BioStar GeForce 7300LE Video Card.
So, Yesterday and Today (June 24th & 25th) were the designated "Big Days" to do the two simultanious builds (strip currently being used computer while assembling the other two)
I fitted the 430 Watt PS into the big case followed by the MoBo with Processor and RAM fitted. All "Spacers" were installed between case and board, new I/O plate fitted to case.. A quick check of the system by "powering up the board" resulted in a "Go" beep from the board and both the LED1 and LED2 on the board lit up.. CPU Fan. NB Fan and two Case Fans were running "hot, straight and normal".. I was tickled pink..
I turn my attention to my son''s computer, called the the Number Two build.. Fit the 350 Watt Power Supply into my "old" case (three 5.25" & two 3.5" External and three 3.5" Internal Bays) followed by the Motherboard, with Processor & Ram fitted. A Check of the system produced in disappointing results.. Pushing the Power Button on the case results in a "one second burst" of power.. LEDs flash, all Fans Spin up (CPU & Two Case) and it goes dead. I "reset" the Power Supply (turn the "master switch" off and back on) and retry.. same results. Took the 430 Watt PS out of "my" unit and tried it, same results.. took the old 350 Watt PS that I had been using until today and tried it, same results.. Conclusion: Something's Dead.. I haven't a clue as to what. The only Possibilities are the Processor or the Board..
I moved back to "my" computer.. I fitted the CD Burner that I'd been using as well as the "new" 250 GIG Hard Drive (that I bought but put into my old case, reformated and installed a Brand New (never been used) copy of Win XP64Bit), hooked up mouse, keyboard, monitor and speakers in prep for configuring the BIOS, as required, updating Drivers, etc.
I got nothing!! the scree flashes, blinks a BSOD so fast I'm almost not sure I saw it, brings up the AMD Logo Screen with "Post" and BIOS" options, if one is quick enough on the "Tab" or "Delete" buttons.. if you miss it, it runs thru the "Boot-Up Cycle" again.. Got into BIOS, configured to Boot off CD, HDD Enabled and all other Drive disabled, hit "Save & Exit", the computer went into boot-up cycle again.. Eventually, I put in the XP CD to see if it would boot off that.. it "recognized" the CD then started running the Load Program.. I figured, What the Hell?" and let it go.. it reformated the Hard Drive and installed XP Pro.. It cycled thru this action three times, each time giving some prompt about it not working (it blinks on/off so quick, I couldn't read it!) before I got tired of doing nothing for several hours!! (after I fitted two other known to be working Hard-Drives.. same drill.. they either "aren't worling" or, if the CD is in the drive, goes into download mode. Once one hard drive appeared to start booting up.. the screen read "Loading Windows 98 (old hard-drive), and it sat there doing nothing for the better part of ten minutes!!
Apparently something is wrong with this set-up, as well the only "new" (as in unused by me) parts are the Board and the Processor..
So, what are the chances of buying two bad ABIT Motherboards and/or two bad AMD Processors, or both??
Any guesses, suggestions, spells, incantations, etc. that might be of use to me in making all this expensive junque actually function? If not, I'll be announcing a "Skeet Shoot" (12ga or larger.. Only! 6ga Punt Guns prefered!), using computer parts as targets, in the near future....
Chas.