Windows 7: Hardware upgrade now Win7 Ultimate won't boot

I have upgraded a machine from an Intel motherboard to an ASUS P8H61-M LX. New CPU and RAM. Before installing the new hardware I changed all drivers to standard drivers, did a system image to an external HDD. After installing the new hardware Windows hangs with 4 little colored dots on the screen (start of win banner?). A safe mode boot stops at classpnp.sys. The same thing happens if I try to boot from the WIN CD. I went back to the old hardware setup and tried to do a sysprep, but that failed with fatal error, but no more info. The HDD is set to IDE, using a PS2 mouse and keyboard. I cannot do a clean install as there is some very old software on the machine. Anything else I can try?

Did you read and go by this tutorial. It may help with running sysprep. Particularly read the very last part of the tutorial, I think it may be why you got the fatal error message. I have used this tutorial a couple of times and it works like a charm, as long as you follow it exactly.
Windows 7 Installation - Transfer to a New Computer