Cycles between on and off when charging topic

Hi Guys

Hopefully someone can help. took my phone out of my pocket this morning to find it off. Thought the battery died but when I plugged the charger in and it just starts up till the Sony logo (and red led) then crashes, continuously. It hasn't stopped doing that. Tried plugging it into the pc to run Flashtool but it doesn't have time to recognise the device before it shuts down again. Reset button, soft reset and Hard reset have not worked.

Please help someone, need a guide or instructions here.