If you have no fuel pressure, the issue is not the SKREEM.

Put a fuel pressure test gauge on the fuel rail, turn the key ON, and see if you have 58PSI. The RCM has a relay that feeds power to the fuel pump, it is triggered by the ECU, if the relay closes, you will (should) have battery power at the output of the RCM, if you do have power but no fuel pressure, replace the pump and filter/regulator.

If you want the SKREEM/ECU fixed the RIGHT way, contact James or Josh at The Mercedes Swap Shop. But beware, if the car has been modded as you say, their base price to have the SKREEM disable is going to to up, as you have unknown mods to the car, unless they can figure out what was done.