Login page stop working

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Hi
We have made a c5 testing site so client can approve stuff/updates before going live.
It was working proper and suddenly the login page stop working and I have tried all our login details and none of those works.
We have also roll-back our recent changes we have made on that site. Also changed the login details on DB but nothing is working for us.
Please if someone can help!!

site: legalwise.amorphousclients.net

Thanks & Regards