Disappearing Windows: Problems recovering from Blaster Infection

My sister's Dell 4600 P4, running XP Home Edition and NAV 2003, became infected with the W32.blaster worm. We were able to remove the infection by applying the FixBlaster.exe tool from Symantec.

However, now we have another problem. Our efforts to apply the Microsoft critical update for the Blaster vulnerability, to update the NAV virus definitions, and to scan for other viruses fail because, when we run these programs, the windows in which they run will only stay open 5-10 seconds before disappearing completely. For example, running the Blaster patch program (the file WindowsXP-KB823980-x86-ENU.exe), the wizard that runs will only stay open about five seconds. If we act quickly and click "next', we sometimes get to the next window (the license agreement) and even, once or twice to the third step, but always and eventually the program window disappears and we can proceed no further. The same thing happens when we try to run NAV (either the main program or just the Live Update portion.) Because of this closing-window problem, we cannot run NAV 2003 at all, so we cannot scan for other viruses or update the virus definitions (which, fyi, appear not to have been updated in 6-7 months - yes, Oy!)

Some other programs on this computer do not exhibit this window-closing problem; e.g., MS Word 2000 seems to run OK.

Does anyone know the reason for the disappearing windows described above, and how to fix this problem?

Thanks, in advance for any help you may be able to provide.

TAH