Okay, back to the original problem...
First (and assuming that playing with the power supply voltage switch didn't kill something), have you put the RAM modules back exactly as they were before? Some boards require certain slots to be populated first, or they won't boot. Make sure the modules are all seated solidly, as well as any other cards (video, etc.)
Second, you can try doing a CMOS reset - check your motherboard manual, there will be probably a jumper on the motherboard somewhere for this. You just short the designated pins for a few seconds to clear all the BIOS settings.
Third, if it still doesn't power up, try unplugging the drives and any other unnecessary components - this will help narrow down if it's a power issue.
Fourth, IF you get it to boot, you can try doing a "repair install" from your Windows CD (assuming you have a proper Windows CD, rather than a "recovery" CD).
Fifth, most software, especially larger packages like Photoshop and Flash, you can't simply "move" to another system, as they create numerous registry entries, update some system files, and place other files of their own in different locations. Your actual photos and other such "project" files can be moved over, and you may be able to migrate your customizations, but the programs themselves will have to be reinstalled from your original discs (or legitimate downloads) if you're going to a new system.
Now if it's just the motherboard, it's likely possible to just put a new board in, or to move your hard drive(s) to a new machine, and have things work as before with some slight tweaks. However, if your machine was badly corrupted with viruses, I'd suggest it's a good time to back up everything important, then format the drive and reinstall everything fresh. You do, of course, have proper legitimate copies of Windows and all your software?