Don't get this trouble with a PC running Windows!
Steps to fix Mac problems (in general - this is pretty much a go to list if something weird starts happening)
After each step retry your task - if it fixes it then you don't need to continue with list but apart from losing program settings this list does nothing dangerous.
1. Check software updates - Apple menu, software updates... - install anything it finds
2. Repair permissions (disk utility, select boot disk, on the first aid tab select "repair permissions") - some Mac experts recommend running this weekly. You can get apps that do this automatically.
3a. If it's Photoshop or Elements then trash the preferences - hold down option, command and shift as you start PS - this will delete most of your program settings - it will be like a new install
3b. For anything else delete the .plist for the app - note that this will lose you all your settings for that app.
4. Zap the PRAM. Turn off Mac, turn on while holding Option P and R until you hear 3 chimes (like the usual 1)
Pretty much that will fix stuff. If it doesn't then you can ask for a free appointment at the Genius Bar at your local Mac store to diagnose it.