I have done a search on the forum and couldn't find anything relevant so apologies if there is.
I'm running an Intel Pentium D with both cores running at 3.20Ghz. I was running an AMD Athlon x64 4200+. (Yes, I do have a new motherboard).
Now, ever since I upgrdaded when I open certain programs the CPU won't do anything and the program won't load. If I leave it for a minute or so it'll just load up fine. I was wondering if there is some sort of driver/program I can install to make this work correctly.
did you install SP3 separately after installing Windows XP? If so try rolling back / removing SP3. I know from experience that Pentium D Dual Cores run well on SP2. I'm not familiar with SP3 but it sounds like something similar to problems with Vista... checking stupid things before loading a program.
Other than that, if it is a 64-bit installation there may be compatibility issues with the programs you're trying to run.
It shouldn't be impossible to roll back. If SP3 is like SP2 is you can just uninstall it from Add/Remove Programs, if you installed it via Windows Update. At least that's what I was able to do a couple years ago with SP2 when someone I worked with had just installed it and it made her laptop slow to a crawl.