Can't start XP virtual machine

I'm using Windows XP SP3 in the virtual machine setup that Microsoft
supplies with Windows 7 Professional. A problem has started suddenly -- I
have never changed a default setting!

1. When I try to resize the XP window, the machine starts churning and
displays, "Enabling integration features..."

2. After a while a dialog box comes up, saying, "Integrated features have
been disabled."

3. I click the OK button, and get a new sign-on type box that says, "This
computer is in use and has been locked" and demands a password. I don't
think I ever set a password and have any idea what it is.

4. After this, if I close or hibernate the VM, when I re-open it I get no VM
window at all, just the "Enabling integration features..." message and the
rest. If I reboot the physical machine, I can sometimes at least get a VM
window the seems to work right, but obviously I can't resize it.

Any advice will be greatly appreciated!