I got it too one night on both my laptop (XP Home) and desktop (XP Pro)
simultaneously while crashing the internal network (computers couldn't see
each other) but leaving the internet gateway open. Got a suggestion that
helped and it was all caused by one file. Now, this file was acting
funny... an MPEG of a TV show I captured a while ago, sitting on the
physical drive of the desktop. From the laptop, across the network, I
tried to move it to a diferent folder. I was told "access denied, another
user or program has control blah blah" but nothing else was using it. Then
the laptop went to 100% on explorer.exe and started running about 200 page
faults per second. After a few minutes it was over 250,000 page faults!
I went to the desktop, opened up windows explorer to the media file and
tried to change the security settings to take full control of it, but got
the same message and same result. I thought virus and had all PCs on teh
network scan but got nothing 3 hours later.
Per advice to another user, I shut down everything, booted into the desktop
into safe mode and just deleted the Tv show MPEg. Turned on all and it was
all good. I think there was some cache problem with that file and it
caused explorer to loop endlessly. I reason that any damaged file may
cause a similar loop, so troubleshooting could be a nightmare but if you
can isolate it it may help.