1. Close all inactive apps in the Task Bar. Double-click the Home button and hold apps down for a second or two. Tap the minus sign to close app.
2. Hold the Sleep and Home button down for about 10 seconds until you see the Apple Logo.
most of the apps from the appstore are designed for the newer iPads.
They will run on your iPad 1, but the iPad 1 isn't fast enough - that's why the apps close unexpectedly.
You should think about to buy a iPad 2 or later...
Sorry, that I couldn't help you