[King Mustard]

Was watching a video until it died.

It has been plugged in for hours since it powered down, so it should be fully charged.

I have held the power button down for 30 seconds but nothing happens.

When plugging it in to a computer, there's no response from either side.

Any suggestions?

[mustang7757]

Leave it plugged in a charger for few hours

[blackhawkhot]

Leave it plugged in a charger for few hours

Make sure your using a 3 foot long cable; longer ones fail erratically to charge even though they provide some current. The USB standard length is set at 3 feet for good reasons.
Try another known good charger and cable if possible.
If it won't except a charge even then it sounds like a power controller or battery pack failure; not your fault.

You can't destroy a LI pack by discharging a phone to "0%" , the phone battery controller plus the pack's on board controller will shut it down before it reaches the pack's critical voltage.
However if left like that too long, days, weeks, the pack will eventually hit this threshold voltage by self discharge which will render it useless.
Higher temperatures will increase self discharge rates.
This won't happen overnight.

[King Mustard]

Leave it plugged in a charger for few hours

It has been charging for 48 hours from the mains.

I also tried holding down the power and volume down buttons together for 10-15 seconds while plugged in. Didn't do anything, either.

Make sure your using a 3 foot long cable; longer ones fail erratically to charge even though they provide some current. The USB standard length is set at 3 feet for good reasons.
Try another known good charger and cable if possible.
If it won't except a charge even then it sounds like a power controller or battery pack failure; not your fault.

You can't destroy a LI pack by discharging a phone to "0%" , the phone battery controller plus the pack's on board controller will shut it down before it reaches the pack's critical voltage.
However if left like that too long, days, weeks, the pack will eventually hit this threshold voltage by self discharge which will render it useless.
Higher temperatures will increase self discharge rates.
This won't happen overnight.

I'm thinking it's a hardware failure.

[blackhawkhot]

It has been charging for 48 hours from the mains.

I also tried holding down the power and volume down buttons together for 10-15 seconds while plugged in. Didn't do anything, either.

I'm thinking it's a hardware failure.

Hard to say. If not dropped or overheated maybe not.

Cables fail a lot especially 3rd party ones. The >3 foot ones fail "silently" as they will connect but supply little or almost no current for charging. Seen this happen 3 times with different brands over the years

The OP should inspect the phone jack for damage or foriegn debris...

[mustang7757]

It has been charging for 48 hours from the mains.

I also tried holding down the power and volume down buttons together for 10-15 seconds while plugged in. Didn't do anything, either.

I'm thinking it's a hardware failure.

Have you tried different cables /charger?