it happened again...

Ok this is hard to explain and hard to understand, mainly because with all the experience and training I've gone through, I've yet to come across a problem like this. Please try to stay with me:

This is my sixth self-built computer. The computer worked for 2.5 years just fine. The last day of college I packed it up (the same way I usually do) and brought it home. The trip is about three hours. I got home that night and hooked up the computer to find it boot up, but not post. There was no signal to the monitor. However, I could hear everything working properly. I could hear the hard drives spinning, see the fans running, hear the floppy drive initiate as well as the cd and dvd roms. Everything was fine except there was no signal to the monitor and I didn't get the usual single-beep during post. My first though was to remove and test the video card. I did so, first removing the card and restarting. This also tested the motherboard and CPU connections as I got the correct beeps for video card erorr (which should have occurred since the video card was not present). So, knowing that the motherboard and CPU weren't the problem, I continued. I then bought a new motherboard, power supply, and video card, installed them along with everything else, powered up to hit the same problem. I replaced the CMOS battery, cleared the BIOS, and reinstalled all the parts (again). Powered up and everythign worked fine. Windows booted up and I tested both hard drives, all the components, and got no errors. This computer ran fine (in fact, great) for the past three weeks. Then, two days ago, the power went out in the house and the computer turned off (what I was afraid of the whole time). I tried to turn on the computer and the exact same thing happened again. I redid everything I did before to make it work again (CMOS battery, clear the BIOS, reseat all the components) and yet this problem still stumps me. I've done searches online and stuff only to hear the same thing, "check the PSU, the CPU connections to the mobo...etc etc etc" and none of it is correct. Is there nobody out there who has had this same problem? Is there nobody out there who can help me diagnose this stressing situation? I have some freelance work I need to do and I really need this computer working. For those of you who need to know my system specs:

400 watt PSU
1400 MHz AMD Athlon
512 MB Crucial PC2100 DDR RAM
1 HD: 120 GB 8MB Special Edition HD
2 HD: 30 GB HD
CD-RW ROM
DVD ROM
ATI Radeon 9600 Pro 128 MB DDR
Creative Labs Live 5.1 Sound card
Standard 56k modem
1394 Firewire card

Like I said, these parts were working fine the past three weeks. Is there a possibility one of these parts could cause the system to not post to the video?

Please keep in mind that all the parts mentioned above were tested in my brothers machine and work just fine. I was thinking it could be something shorting out the motherboard or video card, but why would that happen to two video cards and two motherboards in a row? Please help!?

Thanks!

cmon folks! i know this is really weird but i need some help!!

I assume you were plugged in to a surge protector? The power outage could have made a small surge, which could definitelly have messed things up in the computer again, independant of the first problem.
Does anything different happen if you hit the reset button after starting up?

yes i use a surge protector on everything in my room in fact. ok, so when i power up i hear fans, hd's, floppy, everything power up but the computer will not give the 1 beep nor will it initiate the video (monitor stays at standby). I've tried using another monitor to no avail. ive stuck my video card into another computer and it worked, same for the motherboard. im not too sure on how to test the RAM...? if RAM is starting to go bad, would this kind of thing occur? What about the processor? i know the proc is working because without a video card i get the correct beeps for video error or no video at all, which means the mobo is communicating to the CPU and visa versa...so my only other question is the RAM. I'm the only guy in the house using DDR, everyone else is using nasty EDO or SDRAM...and i dont have any other computers, neighbors, etc to try... ive got crucial RAM and they have a lifetime guarantee, however, im not sure if it applies, three years later... is RAM even the problem? like i said, i have tested all the other hardware, with exception to the ide drives and such, and they all work fine. i haven't tested the ram yet because im not sure how. all my guesses have been made invalid because all the hardware works fine on other computers.
when i press the reset button i can hear the hd's slow down again, then speed up (just like turning it on), and the cd rom/dvd rom lights come on again (like turining it on), etc. just no POST and no video.. its really weird... ???

any suggestions??

Check your CMOS jumper, be sure its set correctly. Take out everything not needed, leaving just the ram, vid card, hdd and try there. Be sure the mobo is screwed down completely. Try a different cpu if you can, that could still be the problem. Trying other ram would also be good if you can get some.

the CMOS jumper is set correctly. ive even cleared the CMOS a few times; left the CMOS battery out for 24 hours; unplugged the ATX power cord from the mobo (it tends to retain a charge)...all of it. ive booted it up barebones, tested another CPU (a faster one). ive booted it out of the case on the original cardboard box it came in... everything. ive got some more RAM coming in from Crucial (thank God for their lifetime warranty eh) on friday so we'll see if that was the problem. i just dont understand though...what else could it possibly be if it's not the RAM??? ive seriously tested all the other hardware in my brothers (this) computer and it all works fine. has anyone else heard of this before or expereinced this before? ...so weird...so frustrating!!!

any other ideas or things i should try?

Ok, after a week and a half of troubleshooting and stress I've finally discovered what causes this and how to fix it. (It's simple really...so simple it's almost sad). I've come across several forums with users experiencing the same problem with almost all of the forums being of no help. It seems that no one could figure out what was going on. Here is what I've discovered:

I was using an ATI Radeon 9600, a 4x/8x card (AGP 3.0 with 1.5/.8 voltages) while my old motherboard was AGP 2.0. So, when the BIOS doesn't pass the POST and doesn't pass signal to the monitor it's because the video card isn't 'talking' to the motherboard due to incompatibility. So, now I have two perfectly good and working motherboards sitting around and I just ordered and installed a new Abit NF7-S board which has the 4x/8x AGP slot, fully compatible with my (and all future) cards.

Whew! Hope this helped someone...