[Richard_Lincoln]

Sounds like a fuse. Why did you disconnect the earth strap? Were you doing something on the electrics?

 

[Richard_Lincoln]

I know that in my audi you have to ensure that all the cars ecus are in sleep mode before disconnecting the battery, otherwise a whole load of problems occur. Could this have been the case when you disconnected the battery? If so the system may have to be reset as it may have interpreted your disconnection as an attempt to steal. I don't know.
You could try opening the bonnet, the leave the car for 5 minutes (for ecus to go to sleep). The disconnect battery. Leave for 20 minutes. Reconnect battery. Leave for 5 minutes. Close bonnet. Now try. (Could also be the key. Could you try another?).
Other than that I don't know of the reset procedure, other than by a dealer.
Any battery issues, unless it was really quite new, would in my eyes warrant a replacement. Your initial problems would indicate this.

 

[Richard_Lincoln]

Well done.