Changing too much at one time can sometimes get a person in trouble. There are just that many more things that can go wrong. It gets had to troubleshoot via forum messages. Plus, if you had one bad new component, it might have harmed what you have elsewhere. Now, with a bad couple of components, it becomes even more difficult to figure out what's wrong.
I see that you tried to get back as close as you can to what you had before all this upgrade. But you are ignoring reverting back to your old power supply. Why? You can temporarily plug in the old power supply without needing to screw it into place.
For now, I would troubleshoot by getting all not needed parts unplugged. Get it down to just a power supply, the motherboard, minimum memory, and a video card (only if there is no integrated video). You don't need drives, or a case, or a mouse, and a few other nonessentials just to see if the board can start up. Once you get that proved, start adding one component at a time.
It is the slow and sure route.
this is my first time ever upgrading more than 50% of a computer (and it happened to be my own computer). i had a HP Media Center m1270n that was bone-stock, but then i decided to buy a new case for it, along with new processor (e4500), cpu fan/heatsink, vid card (8600GT), and ram. i'm using the same mobo as before, however. it was working fine before the swap, but now, when i turn it on, all the fans and hard drive and optical drives physically turn on, but there's nothing showing up on my monitor! it's quite frustrating, actually. at first i thought it was a vid card problem, cause i DID forget to uninstall the old drivers for the old vid card (ati radeon x300se). but when i put the old card back in, it still didnt show a picture. i changed the processor back to the old one as well... no help. oh by the way, i got a new psu with the case that has higher capacity (500W versus 300W), i don't think that caused any problems...
mobo - asus ptgd1-la (pufferG), i915 chipset
ram - 2GB PC3200 (2x512, 1x1GB)
processor - (old) intel pentium 4 530 (3.0 GHz, 800 MHz FSB), (new) intel core 2 duo e4500 (2.2 GHz, 800MHz FSB)
vid card - (old) asus x300SE, 128 MB, (new) evga 8800GT, 512 MB
hard drive - (im using my old one) maxtor 250GB, 7200RPM
(btw. i don't want to buy a new mobo, cause that means new windows, and i don't really want to spend more than i already have.)