Odd XP problem

[Uncle Yuan]

We have several people in our house and have four user accounts set up.  A couple of days ago, with no precipitating factors we can identify, the user account system stopped allowing us to sign on if another account is already signed on.  We used to be able to just leave the computer, after a few minutes it would go back to the sign-on screen, and anyone could sign on even though someone else was already logged on.  Now we just get a little flicker of whatever desktop is currently logged on and then back to the sign on screen.

Any ideas?

[Epimethee]

Out of memory? Each session keeps apps etc. open, so the number of concurrent loggings is probably limited.

[Uncle Yuan]

Nope - since we've had to completely log out these last several days there are no programs running on the other accounts, and rarely anything on the one we're trying to switch away from.