OnePlus 3 not responding

I recently replaced my OP3 battery after facing battery draining issues. Since then the phone has not turned on. The power button+volume down is also not working. But when I try switching it on with the charger plugged in, the OnePlus logo splash screen appears for a while and it switches off again. I can’t figure out what the problem really is. Need help ASAP.

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Look carefully if you forgot to connect some cables or un-plug and re-plug connectors inside the phone.

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