Hello Mark and welcome to the forum;
Couple of things;
1) Have you tested the old psu,here is a psu tester click here can be found cheaper.
2) There is a chance if the old psu went pop it could have damaged or blown the motherboard.
First thing to try,is remove all connected optical drives and one of the hdd's and try one stick of ram and just the hdd with the os connected.
When you installed the cpu,did you apply thermal paste/compound ?
Did the fans all spin,especially the heatsink fan and psu fan ?