First try to reinstall the wallet software.
If the wallet still crashed then the following operation may solve the problem.

You will have to delete the blockchain and auxiliary files in the hidden directory. But since that is a “hidden” folder you need to perform some special actions. First, close the wallet of course.
1) Open dialog box “execute” (windows key + r)
2) Type in the input field %APPDATA%/Gulden
3) Press OK.
4) After this, the file manager will open in the correct folder. Delete the contents of this folder and any folders below it, EXCEPT THE FILE WALLET.DAT
After that you can restart your wallet and the wallet will load a new version of the blockchain. Now it does need to sync normally, this takes 15-60 minutes. But do all this only after you are sure you have the recovery phrase in your possession, just in case.

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