unable to open app store

What happens? Is it crashing?

Try resetting:
Hold both the home and power buttons at the same time until the Apple boot logo appears. No data will be lost.

Try:

- Reset the iOS device. Nothing will be lost

Reset iOS device: Hold down the On/Off button and the Home button at the same time for at

least ten seconds, until the Apple logo appears.

- Unsync all music and resync

- Reset all settings

Go to Settings > General > Reset and tap Reset All Settings.

All your preferences and settings are reset. Information (such as contacts and calendars) and media (such as songs and videos) aren’t affected.

- Restore from backup. See:

iOS: How to back up

- Restore to factory settings/new iOS device.