How do I fix this problem when I'm trying to save for web and devices in Photoshop CS5?

This is why you don't install Photoshop on netbooks.

Try this:
- Activate the Preset dropdown without actually picking one (click the arrow twice) to put your cursor there.
- Press Shift+Tab three times to put the cursor on "Save".
- Press Enter or space bar.

The "Save Optimized As" dialog should appear, allowing the file to be saved. (It is also four Shift+Tabs back from the file format box.)

If it doesn't, then it's for the same reason the regular "Save As" dialog doesn't. Your only other option at this point would be to try hooking up a monitor to your external video port.

Well, first, save the file!! Just save it as a psd with all the layers, transparencies, etc. Then you could restart and try to use Save for Web. You might want to go into the Window pulldown menu --> Workspace -> then reset anything you can reset (unless you have some very customized stuff you want to keep). Screen resolution mentioned above could help. Were you connected to another display or projector or something? If the computer thinks it is still there it will send windows off the edges. A restart would clear that.

What about your screen resolution?