This one is quite an old question, but answering in case anyone else finds this by googling.
When the machine stops and both lights flash, it means that it has overheated. This usually happens on the z8220 to z8280 range when the cone in the dust container is blocked, the twin filters are dirty, or the is something caught in the section between the 2 filters (access this section by removing the filters and then popping the small plastic cover out using the one big clip). After a few hours unplugged it should be ok to use again.
If it does not reset on its own, it will need to have a reset tool plugged in to the main circuit board. Only Electrolux agents (and me, as I used to be an agent) have this reset tool.
Hope this helps
Do you put it down before you turn it on? some vacs wont turn on in the upright position. Happened to me once til I stepped on the button to bed it back then powered right up.