iphone apple logo then blank screen when trying to turn on

It happned on Sunday and is happening again today- suddenly my screen went black (like it was out of battery) and wouldnt turn back on. The apple logo is constantly flashing but then it is doing a big coloured flash and then going back to black- this is constant. On Sunday my phone just turned itself back on after 6 hours, but it doesnt seem to be doing that today.

I have tried the restart but that does not work.