You have probably measured voltage rails so that CPU, memory and chipset gets the juice they need? It would probably be a good idea to measure actual power pins on the slots/chips, not just from the regulator or power connectors incase there are damaged or broken traces.

And as you seem to have scope, also check the crystal so you have a clock. I’d also try to probe some chipset data pins and see if there is any activity and life there (also CLK signals). This could at least help to narrow down where the fault is.

Edit: Batman has dallas, am I correct? It may be that if the battery is empty, the board refuses to boot. I don’t know if this applies to Batman, but there are boards that won’t boot with empty CMOS battery or no battery installed.

Thanks for your input.

I already removed the dallas and checked with another one. I checked clock and Vcc also. I also assume that without one of both, the CPU wouldn't get warm and do anything on the bus...
I'll probe the chipset the next days when i find some time.