Power on, no boot with different hardware

How did you determine taht it isn't a video issue? Have you tried a different video card? Did you try with a single memory module just in case one is defective?

Well, I just tested with another video card and the issue remains. I've tried 4 different sticks of RAM (individually) with no relief. It almost seems like an electrical issue, so I tried a different power outlet, to no avail. I could not be more puzzled!!

Currently, I have the old motherboard sitting on its box with only 1 stick of RAM, the old CPU and its heatsink + fan, and the old video card plugged in. I connected the 20 pin power adapter (the connector on the board is 24 pins, but the one coming out of the psu is only 20 pins, and it used to work) and the extra 4 pin power plug to the board (the vid card does not require extra power). Exact same result. Oh, and if I remove the RAM altogether, it beeps 3 times, like it should.

Next, I will set up all my new gear (mlb, cpu, psu and vid card) on the cardboard box and test. My gut tells me it won't work. Could it be there's some stupid cable or something I'm forgetting to connect??

Help?  

So your old motherboard detects when memory is missing, but it doesn't work when it's installed? That's weird.

What connectors are available from your PSU to the new motherboard? You should have an ATX 20+4 connector and a 4-pin (or 8-pin) ATX CPU connector. Is is what you connected to your new motherboard when using the new PSU?

Ok, did the same test with the new equipment and the same results.

The new psu has a 24-pin connector and two 4-pin ones (the mlb only requires one). I plugged those in, a stick of RAM, the new cpu and video card, and still no video being displayed. I tried that one without any RAM and while it does not beep, the video card's fan does not turn (it does when RAM is installed, which seems to indicate the mlb recognized when RAM is installed).

This makes absolutely no sense, right?

We have all been there at one time or another and it sucks.

I find it hard to believe that 2 diffrent motherboard/CPU combinations would have the same type of problem. My first thought is what are the common parts being used because one of them is bad. From what I have read it sounds like the memory and video are the only parts used in both systems on a minuim setup.

My other thought is your old system has a bad motherboard/cpu and the memory or video card is not compatible (for some reason) with the new motherboard.

In the current minimal setup, none of the parts are common, except for the power cord (though I also tried a different one)! The RAM is common I guess, but I have 4 different sticks and have tried them all individually. I'm starting to wonder if say my original video card was bad, by putting it in my new board, maybe it shorted it somehow?

I had the same thing happen when I changed the RAM in my system - but I didn't change boards.

In my case - pulled CMOS battery for 30 seconds and put battery back in. Presto.

In your case, it sounded more like a power supply problem until you said no RAM causes the 3 beeps. I would still try the CMOS thing.

Have you tried a different video card in the new system?
Because it sounds like a graphics card problem to me...

Thanks for the suggestion. I just tried pulling the battery and the issue remains.  

I just got a new video card today BobfaceBilly and the same thing happens.

I guess it's time to bring it to a competent shop that will identify the root cause of your issues.

Well, for the sake of closure, here's the winning combination: I put in the old psu, reset the cmos, and bam, it was able to boot. I can't put in the new psu though; the same problem happens with it, cmos reset or not. But it now works with the old psu, which is WAY better than how the day started! Thanks everyone for all your input. Guess I'll be returning the psu!

Ahh, glad you got it figured out. Odd that the PSU was bad, those corsair 450's are really nice PSU's.
Anyway its always a nice feeling when you get your dead comp back running.  
Enjoy the new computer

Thanks BobfaceBilly. To be honest, I still don't know what exactly it was that is/was bad. This is the same PSU I had on my old system and it too would not boot, even after I reset the CMOS on the old board. It seems to be some kind of weird combination of defective old board + defective new PSU + CMOS needing to be reset on a brand new board.

Oh Heck - I know what happened - you completely forgot to sacrifice a virgin !.... or maybe it was a pigeon..... I forget, but just use virgin pigeons and you should be good.

Lol yes, now off to the zoo to find some pigeons, hopefully of the virgin kind!