vMax :
It would be great to understand what parts you have i.e. CPU/motherboard/ram/psu model and make..
It should still try and boot. Double check all the connections including EPS/CPU power cables and if you think the HSF is not on properly, hold it down to put a little extra pressure and try to boot as it is all in an open state.....
I am presuming that it is all on a non static surface!!!
CPU - i5 2400
MB - ECS H61H2-MV
RAM - Kingston 2GB 1333mhz
PSU - Generic
The CPU, MB and memory worked a month prior and I layed them off after an upgrade so I can say they work/ed.
On my first test something smelt burning, though I wasn't able to find the source.
Another thing that can be noticed is the CPU fan stops after a few seconds from spinning then starts to spin again.
I tested the system to the psu that runs my current setup (seasonic s12ii) and gave off the same results.
I might've fried the unit during the first run. Just asking if an untightened CPU fan can cause this since it's hard to remove my hsf from my main unit just to test this spare one.
It was tested on top of the motherboard's box and the PSU on a wooden chair.