Hi Bob, welcome to Neosmart Technologies.
Corrupted updates or system files... typically common on pre-vista installed machines. For some reason either MS or the OEMs with thier custom versions have messed up the images they pre-install on thier machines, causing pretty much a mandatory re-install to fix everything and upgrade to SP1. There are some other steps you could have tried in regard to simply getting the install to boot again, such as trying last known good configuration from the advanced boot options menu with f8 befoe Vista tries to load, using system restore from WinRE, or running a command prompt there and running an offline check of the system's files with system file checker (sfc.exe). A new isntall + SP1 should leave the machine running as new with little problems. I've described the hassle i've had with my Dell desktop in other threads in the past, but a re-install fixed everything.