pc restarting while booting up

[mantaman]

hi all. hope i,m in the right section..anyway i,m having probs with my pc, more often than not when i turn it on it gives its single beep then starts loading the windows screen bar thingy then it just restarts gives a beep and off she goes..it usually goes after its restarted once but today it did it 3 times!! if i turn it off once its been on it starts no bother? also once its going it doesnt bat an eyelid? i have been told the case switch could be at fault as they are prone? anyway specs as follows;coolermaster cosmos's' case
p6t deluxe v2 mobo
i7 920 stock clocks+cooler
6gb ram corsair xms3
corsair hx1000 psu
1x gtx 580 zotac
its a self build approx 2 1/2 yeaars old no probs until now...recent changes are--went from sli gtx285 to one 580, but this was afew months ago with no probs straight after..more recent i upgraded my drivers for logitech g15 keyboard and g35 headset..any help would be great thanks...ps.. i have checked all connections and seatings no differance

 

[Matterez]

Dodgy power button on the case? Just a guess from the info...

 

[phil-k]

you could try removing the m/b connector to the case switch and short the pins with a screwdriver to start it for a while to see if its stable.
If it still does it, its obviously something else