On homebuilts I find that the BIOS must be noted to be Vista compatible (and the hardware too.)

But your post wrote nothing about motherboard and other non-Microsoft supplied drivers. Some builders stop installing drivers when it works and the most common missing driver is the motherboard one.

Without those drivers, odd crashes are not uncommon. That and heat induced crashes.

Try a little more about the install and if the case cover is off or not.

Bob