First time poster, so be kind....

Assembled a new pc last night, and upon completeing assembly, decided to at least check it posted, before stopping for the evening.

On initial start, the machine started, and proceeded through the normal start up procedure.... at this point I turned the machine off, and grabbed myself an old ibm keyboard I had lying around.

Plugging in the keyboard, I started the machine again, but this time it would start, spin the fans to full speed, before slowing to idle (as before) but then simply died.

I proceeded with some trouble shooting at this point that included me..
resetting cmos
unplugging keyboard
transferring power lead to another power socket in the hallway

I would find the machine would start fine with nothing attached, and turned on, but the moment I turned on the screen and attached a keyboard, before turning on the machine it go back to the start-crash behaviour.

Deciding at this point to take a break, I subsequently decided that possibly my issue may be too much thermal paste, so I removed the heatsink, removed the paste, and reapplied a much smaller amount.

On connecting it to the power again, and hitting the power button, it started to post, and on checking the screen (turning it on) the expected details were displayed.

I turned off the pc, connected the keyboard, and fired it up...... back to the start-crash 

i then tried a usb keyboard (suspecting it was a keyboard issue), and no luck...

At this point, something dawned on me... 

I turned the machine back off, reset the cmos, and turned off the monitor, leaving the usb keyboard attached... and hit "on".

The machine started up, and kept running... turned on the screen, and watched it proceed through to "system disc needed".

I then repeated this, and again it started fine, and I hopped into the bios to start configuring, and completed that with no issues.

So via testing it definitely appears the issue is related to the monitor... or is it something else, and this is only a symptom?

Some monitor details -
- The monitor is an existing Samsung one, and has worked fine for at least a year, albeit as a secondary for a laptop.
- The monitor is attached using a vga cable with a vga/dvi adaptor

I'm a bit puzzled, and having searched online can't seem to find anyone suffering the same issue where the monitor being off, allowed the machine to post, but with it on, seems to cease the process.  But that once posted, the monitor could be turned on quite happily.

Thoughts and suggestions? 

NB/ the mains fuse for the circuit also popped a few times, while I was doing all this, so is it possibly a psu issue?

PC details
MOBO - GA-x58-UD3R
CPU - Intel i7 930
Case - Cooler Master HAF 932
HDD - 2x WD Black Edition Sata 3 1tb
DVD - Samsung SH-2332 (?)
Video - Zotac GTX480
CPU cooler - Prolimatech Megahalem Rev B
CPU fans - 120mm Gelid PWM fans
PSU - Antec Quattro 1200W
Memory - G.Skill DDR3-2000 3x2gb