Why can't I open some installed apps and I can't download new apps?

I have a big problem. I have installed some games and some other apps, and everything works fine. But now the apps doesn't work... only works system apps and FB Messenger. I can't open other apps. And for example MS File manager is named like @{Microsoft.MSFileManager... Do you have any ideas how can I fix my phone? and the phone is low end Prestigio MultiPhone 8400 DUO. Thank you for help.

Sorry for bad English. I am not from english speaking country.. :)

Oh, and I forget.. It is Windows phone 8.1 OS version: 8.10.14219.341 ... And I can't downloading apps.. It stucks on pending.Attachment 93002

Are the apps which not work on a SD card and the apps which work on the internal memory?

Yes, apps which not work are on SD card, because the phone has small internal storage.

What brand and class is your SD card and how much space have you left on the SD card. It's a problem with your SD card.

It's a SP card 8GB.. It means Silicon power I think. It's class 4 and free memory is 2.09 GB.

You should at least use a class 6 and even better a class 10 card. And use a good brand( SanDisk, Samsung, etc) But if you want to keep this card then format it in your phone and reinstall the apps but if it happens again get a new SD card.