Thanks for all your tips guys!
I have tried a different monitor, but the test pattern I mention is the one which states "The monitor is working correctly, check your PC and your cable are connected."
As far as the beep patterns, I don't get beeps. I have tried reseating the CPU to no avail.
I run the machine through a UPS so I don't believe its a problem with surges or power spikes. As far as dust goes I do take the case off the PC once a month for a blast of canned compressed air - I live in a very very dusty environment!
This system does have an overheat protection for the CPU (all geared up for overclocking - but never got the chance to try that out!!), but the fan is connected and working and no obvious damage to the heatsink either.
Either way it looks like it might be a trip to the computer doc next time I venture back into civilisation.