no post power cycles

[matt88]

Help, recently took my custom build pc apart to dust out and install a water cooler.

 

Now it won't POST. It powers on for 8 seconds then shuts down and tries again in the same cycle, there is no screen output. Have I got  something plugged in the wrong place? Everything lights up and all fans spin.

 

I'm sorry if this has being posted before but I wasn't sure what to search for.

 

Do I need to let it cycle whilst the new cooler settles in?

 

Build:

 

MSI z97x gaming 5

Core i5 4690k

Cooler is coolermaster masterliquid lite 240

GPU is GTX 970

Case NZXT H440

 

Thank you in advance.