I turned the bottom oven on and it was like a small lighting bolt went off, it tripped the fuse box to the house and now only the top oven works?

You will probably find that the element for the lower oven has expired. They sometimes do go in a shower of sparks. I once had an element on a hob explode in my face and a small lump of red hot metal flew up and just missed me.
It is easy to get to the circulatin fan and element, you just have to remove the 4 self tapping screws in each corner of the fan/element cover for the cover to come off. If the element has burnt out as you say you should see some evidence of burn marks/holes on the element.
The bad news is that you will have to take the whole oven out of the housing to remove its top and back to gain access to the element retaining nuts and the wiring to unclip/reclip it.
Try espares for a replacement element and if it was a major bang when it went, you should consider replacing the thermostat as well as this is often damaged by the element going.
(The thermostat is the long thin metal rod in the top right hand corner of the oven and is connected to the control by a very thin fragile pice of wire - be careful)!