Hi guys, just bought a 98 xh v8 spack and I stupidly unscrewed the bracket and earth cable for the ecu to remove a speaker wire. The battery was still connected and know it wont start. I left it sit with ignition on for 45 mins and it started but if I leave it sit it won't start again. When I turn ignition it clicks and the fuel pump goes and this symbol comes up on the dash (!) Have I killed the ecu or bcm? Any ideas?

The earth strap on the ECU bracket is just the case ground which is where the shield dumps ignition noise to. It will not effect the ECU in the way you describe. It may be that you disturbed some other connection whilst in that area?

Would disconnecting the power lock actuators have something to do with it?

Well you do need to wait til they cycle, so would be handy if they were working.
From memory, if you don't start within that small time period after, you need to repeat the cycle next start, as codes won't have downloaded to the BEM.

The whole procedure is in the tech docos here.