Hello guys, hoping for some help here.

The other day I parked my 2008 Tenere with the parking light on and didn't notice for a couple of hours. The next morning there wasn't enough juice to fire it up so I removed the battery and hooked it up to the optimate. After refitting it I turned the ignition on and got absolutely nothing, completely dead. Obviously I checked all the fuses to no avail and thought maybe the main relay was a somehow broken so tried replacing that but no joy. Not trusting the old battery I got another today, charged it up and..... nothing. Not a dickie bird. I can't believe a connection has been lost or corroded. How can something so critical happen from taking off a battery?

Ideas appreciated as it's my only transport and I'm kinda up **** creek at the minute.

Thanks in advance.