My device is soft-bricked after some system errors Welcome!

Edit: the phone is => Prestigio Multiphone 5451 DUO, android version is 4.2.2

In the past days, I decided to download the larger Messenger app, and removed previously installed "lite" messeger app, and installed facebook lite app, and previously installed the larger FB app. And my phone stuck in a boot-loop. :(

After that, I browsed websites with Google Chrome app, then my phone started freezing with some org.android messages, then accidently the stock launcher is stopped too. I restarted the device, then a message showed up => "encryption unsuccessfull" like in this image



I unfortunately pressed the "reset phone" button, but it don't did anything so I unplugged my battery. Now, when it boot, it stuck in the logo. 

Only thing I can do is to boot into stock recovery mode(vol_up, power and Home), and factory mode(vol_down and power)

I can "sideload" with ADB in Recovery Mode, but can't flash due to android signature? .. //edit: but PC sees the device.
I tried by listening adb on boot with both linux/windows, but they can't detect it.. 

I think someone can help me, I don't want to throw away a whole phone, because others fight with famine and so on. :(

Cheers, LeFizzy.
Flashing the phone should solve the issue but you'll lose all your personal data. 

Download the stock firmware here, Click on Support tab.