I disagree with you there, but to each their own. Let's try to HELP this guy instead eh?
I've had far more issues with XP and hardware changes vs 7, by a huge margin. Honestly I have the OP look into clearing the CMOS if he hasn't already, to make sure it's not still trying to report the original processor ID or something along those lines.
I've swapped CPU's, cloned HDD's, vid cards, and even MB's on Windows 7 installs. Good luck on XP if you do a mainboard swap not having it bug out. 7 would detect the changes, I would install drivers and it was like nothing ever happened. I will admit though that most of my experience with those hardware swaps are more on the Intel than AMD side of things.
As with any major hardware change like the CPU or a fresh MB install, a BIOS clear/CMOS clear is always recommended and should be documented in the MB's manual. Is the AMD chip an APU? If so and you maybe had the GPU disabled, might it be re-enabled and bugging things out? Has anything else changed beyond just the CPU?
Have you tried to do a startup into Safe Mode? Maybe Safe Mode with networking if possible to remove and update the old hardware drivers? Run a ChkDsk, make sure that no major system files became corrupted. Ensure that all data cables are tight, power connections are tight, memory are seated in the slot. I'd check all those and see if you can't get the disk scanned and repaired (maybe use scan /sfc). Maybe if at all possible, going into a system restore may help replace something that was corrupted.
It's very odd to me to see a simple CPU swap cause so many issues to a modern windows install...and I wonder if there is some other cause for the corruption? Maybe re-seat the CPU? I would go through all of those things, to make sure it's all proper, and good to go. You say you don't have a backup of your data, do you have a 2nd pc that you could use to view the data on that hard drive? Or another PC that you could setup for hotswap so you don't have to choose which OS to boot to? It should matter either way, if you can use a sata to usb, esata or just rip the side off of a case and use the internal sata, you could at least backup your data or even run a scan disk to see if there's something needing repaired.
Keep us posted on what you're doing to resolve this issue! Hopefully we can get ya sorted without having to re-install! I also hope you can backup your data and will implement a setup to do so after this experience. It sucks when something like this happens, but there are solutions, we just gotta narrow it down to the one(s) that work for you!