Sounds like there may be something iffy on the device.
Try starting up the phone in "Safe Mode" and see if it loads fine. You won't have access to all apps. It is a restrictive mode, however you should have gallery access (on most devices at least). If it works fine, then you need to check the phone for bad apps, viruses and malware. Even if you can't access the gallery on your device in that mode, I would still check the device for bad apps, viruses and malware. As it is unlikely a system problem when only happening in certain apps.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.