@sunray777,
Please clarify what the problem is. Is it your keyboard that is locked up or the computer screen?
Are you able to see the mouse pointer move?
Consider unplugging/plugging in your keyboard and see if that makes a difference.
If the mouse pointer moves, try collapsing the browser window by clicking on the box NEXT to the X in the upper right corner. That may free up some of the memory resource.
Which browser are you using? If it is Chrome, after shutting down your PC, Chrome will display a message about it not properly shutting down when last used and ask if you want to resume where you left it. Answer Yes. You may or may not be able to navigate back to the screen where you were typing your text.