The standard laptop here is a Dell D600 with XP SP3, which came with an 80 GB drive originally. One of them was upgraded to a 160 GB internal drive. Ghost was used to transfer and expand the original installation to the upgraded drive. All was fine for a while. After some time, the computer boots to an empty text screen with a cursor in the upper-left corner. This is right after POST and before anything Windows-related happens. So, F8 didn't work, safe mode didn't work, and there was no Windows logo. FIXMBR, etc didn't always work. It was necessary to re-ghost the system from backup to recover it. In all cases, it happened after installing either a new or updated software such as Adobe, Picasa, etc. Installing the same software upgrade after re-Ghost is successful.
A virus scan does not show any abnormality. What to look for?