Speaking too soon... (Self-build problems!)

[Jingo]

After praising the past two years of unfaltering use on my self-build in another thread, I woke up to a machine that would not power up whatsoever

After testing plug sockets and power cables and finding them to be fine I noticed there was no light on the psu when connected to a working socket.

After obtaining a replacement psu and setting everything up - I'm still getting nothing, no lights on motherboard, no booting action whatsoever (The replacement psu does not have a light on it to check btw).

This leads me to believe that it must be:

- the power switch connection? (but there's still no light on the motherboard).

- the motherboard has died when the psu went? (There was no 'bang', minor explosion or incident of any sort - the machine powered down as normal on last usage and then simply offered nothing the next morning).

- Something I have missed - it could be something simple or silly I have missed or not known to have checked?

Any ideas or knowledge anyone has would be really appreciated

Thank you