At that point, my only option is to reboot from the button on the front of the machine.
Rebooting *might* lead to the computer being up, but I can't count on that. It might take five or six reboots (including safe mode), and after that, I can't count on it staying up for an hour. It might keep working for days, and it might jam up when I load my first web page.
Rebooting doesn't always work. Occasionally, I get a blue screen--and control-alt-delete doesn't work, even though the blue screen says it will. Sometimes the computer jams in the middle of the booting process. Back to the reboot button for both cases.
Previously, it pretty much just jammed when I loaded web pages, and I learned to be careful about how many tabs I had open. Sometimes, it couldn't handle more than one page coming in.
I got a suggestion to get Firefox 2.0, which helped for a while, but things are getting worse again--including a couple of times recently when it jammed when I'd opened a document, but nothing was coming in over the modem. I consider this to be a scary new symptom.