Using XP Home SP3 and all updates. I am the main user of my pc and logon to
my (Administrator) account. Sometimes a "Guest" or other account user also
uses the pc. "Switching" accounts used to work fine.

There have not been any other users for a few months but now, when we
"switch" to another user, after (I think it is exactly) five minutes, my
account closes down and logs off - all by itself.

Any suggestions on how to stop this happening? (In case it is important, I
would just mention that I had an mbr infection cleaned from my PC recently -
and certainly since the last time anyone else "switched" accounts without any
problem).