A Dell or IBM notebook computer may hang (stop responding) when it tries
to use Standby mode.
This behavior can occur if the COM port is open (by a modem, debugging, or so on) when the computer tries to use Standby mode.
To work around this issue, make sure the COM port is not active when the computer goes to Standby mode.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.