Volvo G720B has gremlins

Greetings from sunny South Africa... I hope someone can maybe help me with an issue we are having with our Volvo G720B - it has gremlins... It goes through phases where it just won't start, but changing a fuel filter or disconnecting the batteries for about an hour sometimes helps - but I think it might be co-incidence. Here's what it does.... It'll swing sometimes slowly sometimes at normal speed and just not fire. Depending on the grader's mood various things are noticed when it won't start. This time - there is no power going to the injectors and there is a fault code about general ECU failure the last time it did this we disconnected the batteries for 2 days, cleaned every plug on the machine and changed the fuel filters - that worked The last time - the diesel was just running through the fuel pipes not pulsing - changed the fuel filters, disconnected the batteries and it came right But this time we are not having any luck on the usual tricks - any suggestions please!!!!