photoshop elements suddenly slow

Try resetting the Preferences:

Restore default preferences Preference settings control how Photoshop Elements Editor displays images, cursors, and transparencies, saves files, uses plug ins and scratch disks, and so on. If the application exhibits unexpected behavior, the preferences file could be damaged. You can restore all preferences to their defaults. Note: Deleting the preferences file is an action that cannot be undone. Do one of the following: • Press and hold Alt+Control+Shift (Mac: Option+Command+Shift) immediately after Photoshop Elements begins launching. Click Yes to delete the Adobe Photoshop Elements settings file. • Go to Edit > Preferences (Mac: Photoshop Elements > Preferences > General), click the Reset Preferences on next launch button, and then click OK. When you restart Adobe Photoshop Elements, all preferences are reset to default settings. A new preferences file is created the next time you start Photoshop Elements Editor. For information on a specific preference option, search for the preference name in Help.

from here:

Preference file locations for Photoshop Elements and Premiere Elements