Hoover HED 6612/1-80 dishwasher all four lights flash and beep whilst the machine drains, after a couple of minutes the beeping stops but the four lights glow. Cannot reset to cancel. Also still makes draining noise whilst the door is opened. There is no water at the bottom of the machine

Not sure if you have got a user manual for this dishwasher. You can download one from this site.

You have a flood situation inside the dishwasher. See page 12 of the manual. There may be no water at the bottom of the machine but there is some overfill occuring. Also see error codes on page 13. This can be either because the flood detection circuit is faulty and giving false trigger or there is water in the base of the dishwasher housing due to leaking door gasket or hoses.

Some things to try. Turn mains power off and back on and see if there is any difference.
If not, then turn power off and pull dishwasher out from the kitchen benchtop. Put a few towels on the floor and tilt the dishwasher side to side on the base and see if any water comes out. Wait 5-6 minutes and turn power back on. See if it makes any difference.