I cannot open applications

Try closing all the open applications. Double click the home button, this will bring up all the apps that are currently open on the dock. Click and hold on one of the apps until you see a red minus sign on all of the apps. Then close all the apps.

Here is a video in case you get stuck: http://www.youtube.com/watch?v=-BpKelKli...

Sometimes what happens is that people don't know how to properly close apps and eventually they have so many apps open that the iOS device becomes super slow and then you start getting problems running the apps. I have seen this many times with my customers iOS devices.

If this doesn't work then try reseting the settings in the settings app under "general"

Another thing to try is hold down the sleep/wake/power button on the top right and turn off the ipad then restart it.