I need more detail, but it sounds like a warning message of some sort has poped up underneath your LW window and stolen the focus.

Frequently, many warning boxes won't let you do anything else until you respond to them, which would explain why you can't simply click on the LW window and get the focus back.

If this is the case, try to minimize LW to see if there is an alert box underneath (two ways to minimize, either from the window itself or right-click the programs' Task Bar button and select "Minimize"). Don't use the "Show Desktop" Quick Launch icon, as it will minimize the alert too.

Or hit Alt-Tab to see if any other processes are running (not Task Manager) and switch to them to see if they are prompting you for anything.

More info is really needed to know exactly what is going on, but since nothing is locking up (mouse does not freeze), this is your most likely cause.