My lumia 520 has stopped working?

Hello!
I have a Nokia Lumia 520 and recently it has been running low on memory. Since yesterday it's functions have stopped working even though I deleted all my apps to free some space. Now, the wifi works, my whatsapp works, bluetooth, ringtones, flight mode, other apps like games, all of these work. But the messsages, contacts, photos, storage sense, camera, podcasts, app store, my email account, all of these have stopped working. Every time I tap on something, it loads, but immediately crashes. I need help!
I even tried to reset the software by pressing volume down key and power key at the same time but it didn't help. Hope this detail is enough for you to be able to help me solve this problem.
p.s when I connect my phone to my laptop it doesn't open anything, like it shows the phone icon on the screen but when I open it, it's empty.

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