Mac Pro shuts down immediately

I got my replacement mac pro and swapped the HD out of the non functioning one into the new one and it works perfectly (so far). Now I am wondering if there is anything I should try differently? Should I move the computer into a different room? Get a UPS? Any suggestions to improve the lifespan of my Mac Pro tower? When I use this computer I am always worried that it will suddenly turn itself off

Congratulations on your new Mac. Maybe it was the temperature of the room that contributed to your problem? Perhaps consider setting up your studio in another room or installing an air-conditioner or heater (as the case may be).

I know this is an old thread, however I was experiencing the same problem; Mac Pro 3,1 (Early 2008) was randomly losing power while on, was near impossible to start up as it would immediately shut down upon pressing the power button. I unplugged stuff, re-seated cards, RAM, replaced the logic board battery (and broke off the metal clip in the process!). Finally ordered a replacement power supply (PN 661-4677) from DV Wharehouse for and it seems to have fixed the problem.....$300 later with much loss of hair!

I experienced exactly this after a period of will it/won't it start with my Mac Pro early 2008. It was definitely the power supply and the Pro worked fine....for a while. I suspect that the power supplies from this time are prone to this problem because I have sourced two 'refurbished' units from Visparts, and both have failed again after approx 6 months' light use - with exactly the same symptoms. I have now ordered a new power supply via eBay and I'm hoping this will last longer. At least new items come with a year's warranty; refurb are 30-90 days depending on supplier. I hope this is useful to others. This link shows how to replace power unit. https://www.youtube.com/watch?v=6lOzC3ovhDk