Intermittent problems switching users

Question

My Windows Vista x64 machine (not joined to any domain) has intermittent problems switching users. Sometimes, for no apparent reason, it decide that the "Switch User" option off of the Start menu or Ctrl-Alt-Del does absolutely nothing. Logging off still works, however, after I log off:

• The mouse cursor is invisible on the logon screen. The mouse is still active, because buttons on the logon screen will light up if I move my mouse around enough.
• There's an "Other Credentials" button below the password prompt that isn't there when everything's working properly.
• If I type my password and press Enter, I get the following error: "A device attached to the system is not functioning."
• Trying to restart the computer (using the "Power" button at the lower right corner of the logon screen) does absolutely nothing.
• Trying to shut down the computer (using that same button) instead puts the computer into sleep or hibernate mode. When I turn it back on, it's still having problems.

So far, the only solution I've found is to hold the power button for 5 seconds to force the computer off.

Any suggestions?

Answer 1

This symptom is caused by some SpyWare. You should scan your system with Malware Bytes and also SpyBot Search & Destroy:

  Malware Bytes
  http://www.malwarebytes.org/

  SpyBot - Search & Destroy
  http://security.kolla.de/

Although I've not experienced this behaviour with virus infected computers, you might as well make sure your Anti-Virus software is up-to-date and run a full system scan with it. If you don't have an Anti-Virus program, I highly recommend this one:

  F-Prot Anti-Virus
  http://www.f-prot.com/

Answer 2

A while back I had a very similar problem, where at first the only solution was to force a power-down, as you did. But I had two user accounts on the machine and I found that if I logged in to the second user, then the first user would start working again.

I had commercial anti-virus and did not find a virus on the machine.

Bad news/good news: never did find out why it was happening / but it was not frequent and eventually went away.