Question

What could be the reason - it is not the charger I think because I have tried a few others but still

Answer 1

Hey MrJoe, the tablet's condition may stem on one of several factors

1. Battery to drained requiring the highest amperage charger it can bear - the original one it comes with is normally sufficient (also, do be sure that the chargers or USB cables you are trying are functional and able to charge other devices)
2. Battery too drained requiring to be boosted - involves opening the tab up to access the + & - terminals and hook live 5V wires for 10 seconds
3. Bad battery (little built-in circuit may have failed) - will need to be replaced
4. A bad firmware/OS may also cause this as well. Especially if the device is detectable by a computer when connected and the power button is short pressed.
5. Bad charging port - This is true if it powers on after suggestion no.2 but still will not charge through a pin to jack method.
6. Bad charging channel - one of the charging system dependencies may have failed and thus retarding charging all together.
7. In the extreme, the surface-mount power management chip may have failed requiring replacement (or the replacement of the entire tablet's system board)