how do i open the door?

What are you doing wrong? You are not searching for answers.

Check the machine is emptying

Check the pump & filter if necessary

See this, which I found in a ll of 60 seconds:

http://www.diynot.com/diy/threads/hoover-performa-900-ac90-001.10797/

http://www.justanswer.com/uk-appliance/4z35j-hoover-performa-1100-wouldn-t-open-programme-ended.html#re.v/491/

http://www.fixya.com/support/t12174854-hoover_performa_900_washing_machine#solution-section

XXX
February 2016