A conflicting tweak possibly - if this is the case you would have to disable all tweaks and re-enable one tweak at a time until you find the culprit.
A Virus Hmmmm
It is not internal damage as the iPad is still working with all stock apps running fine.
Did you sign out and back into AppStore ?
If that did not work then try Resetting Your Device via Soft Reboot, it will clear the memory of the device by killing the applications.
Soft Reboot : Hold the Power and Home button at the same time, when the slide to turn off the phone option pops up, Keep the Power and Home button pressed down untill the screen goes blank, keep them both pressed in untill you see the Apple logo.