if it is a driver issue, it could have been due to, something, somehow,
corrupting a file that's associated with the driver, from any number of things.
Even if you have the 'latest' drivers, you might re-install them just incase.
It could also be that something changes your settings in the bios your the
power saving, or acpi stuff. You might want to double check those settings.
edit to add:
XP is said to over-rider most bios settings, but I have seen it cause trouble
depending on the mobo.