C2 lights issue

[Pricer07]

Just fitted new clutch to car. So had to take battery and ecu out. A nut snapped in the engine so I tried to weld a Nut on it. As I was welding, someone shouted to stop, I asked why and they said the lights were flashing everytime I struck a weld. I earthed the welder to the chassis. What would cause this? Anyway, got everything back together and put battery back on. The side lights front and back and indicators stayed on constant. Went to start the car and with ignition on the headlights came on too. Car wouldn't start, hoping it's a flat battery as it wasn't great before I started the job over a week ago. What have I done or need to do? Any help appreciated.

[GiveMeABreak]

Well first thing is check you battery is good, lots of weird things can happen if it is flat. I've seen someone nearly have a cardiac because of a flat battery - turned the ignition on and all the dials went mad, flicking up and down and lights going on and off etc.
Once you've checked / charged the battery and if you are still having problems, check the obvious fuses first and really check them - as some can look ok but have a fine crack through the blade.
Check you earthing points thoroughly - as by the sounds of it they didn't do a good job! Look for your earthing straps and clean these up making sure there is good contact with the metal.
If you're still having problems, you'll probably need to get it on the Lexia for a check, as you could of fried some electronic components.