Hi again Jamie,
The problems that you are having are typical where a metering valve is at least partially stuck. When you were trying to start it after changing the filters, was there any evidence of smoke coming from the exhaust? If 'no', it suggests a lack of fuel being delivered to the injectors. If 'yes' at least its trying to start but could be prevented by cranking speed too low or loss of compression.
Again, when trying to start have you slackened at least two of the injector pipe nuts at the injectors? Two or even all four should be slackened a little. Turn the engine over until fuel escapes from the nut. When fuel is present tighten the nuts and attempt to start again.
It is quite common partivularly with older tractors that once the fuel system has been disturbed to change filters for example that they present a great deal of difficulty starting the first time afterwards. Over the years I have found that the best remedy for this is to tow the tractor to start it. This of course will only work if your tractor is a non-Multi-Power.
Being towed with your tractor in top gear will generate a higher cranking speed and is normally successful. Will your weather conditions allow this? Do you have access to another tractor?
Remember that a rope and NEVER a chain should be used.
One further check is to ensure that where the stop lever is connected to the spindle going into the pump is secure. They can work loose on the flats and in effect the pump is not fully in the 'run' position whilst you are trying to start the engine.
Let us know how you get on.