Q: Whenever I attempt to apply an adjustment, add a new adjustment layer, or apply a filter, Photoshop "appears" to lock-up, and I don´t see a dialog box.
A: This is most likely due to:
a. a recent change in your monitor resolution; or
b. you´ve worked with more than one monitor and left the dialog in an inaccesible spot on the second monitor.
In the first instance you should clear the apparent Photoshop lock-up i.e. simply press the Escape key! The fix for the missing dialog/palette is explained below
Photoshop remembers where your last dialog box was on the monitor, and so when you reduce resolution, the dialog box will fall outside the viewable area (reported behaviour).
Fix1: Increase your resolution to max setting, create a 'dialog box situation', and move the dialog box to upper left corner of screen. When you hit 'OK' in the dialog, Photoshop memorizes the position, and you can now safely decrease resolution again.
Fix 2: Try resetting your palettes through Window>Workspace>Reset Palette locations. This fix only applies to the Palette location
Photoshop is supposed to automatically place dialogs within your resolution setting, but fails on some systems / situations. It has been marked as a bug, and will be fixed in the next release.
It is recommended to restart Photoshop every time you change your monitor resolution.