profiles getting renamed to *.bak?

For the second time, my main user sign-on has mysteriously gotten
renamed to "D-Lux.bak".
The new folder, which is now named "D-Lux", has very few of my
application settings, etc.
I can't normally rename the user folders, as they're System Folders.
I've run my virus scanner (installed AFTER this happened, as i've only
just completed a total OS reinstall on this machine), and found
nothing.
I've managed to redirect/rename the folders through the registry,
which almost worked, but i've run into various errors concering
folders' locations and such.
Has anyone heard of this type of thing, and if so, is there any other
solution than spending another whole day formatting, reinstalling,
cursing, searching for drivers, falling asleep in my chair, etc?
thanks
Don