Problems replacing my PSU. Questions?

I bought a prebuilt desktop computer last year. It has an ASUS FM2 motherboard and an A85500 APU in it.

I replaced my hard drive due to it making noise and figured I change out the 350watt power supply that it has for my 5 year old 700watt Thermaltake I had in my old dual core which works.

I was reinstalling Win8 and after it was done and I go to log into Win8, the pc would just shut off immediatly. I turned it back on and it did it again but the fans where still going and at full speed. Tried this a few times, even reinstalling Win8 a couple times, same thing.

I then put the 350watt PSU back in it and reloaded Win8 and everything is working good for over a day now.

My 5 year old Thermaltake 700w PSU works in the dual core, but not a low powered new APU pc? Am I missing something? If the power supply has an issue, why only with an FM2 motherboard not a Dual Core? Could it be causing high temperatures?

I just don't get it.

Thanks for advice.
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  1. Could be any number of things, so it's hard to make any definitive suggestions.

    The fact you can install Windows with the PSU but not log in is very strange. This would seem to suggest that things like airflow/cooling aren't to blame, as if you start it "cool" it should work for a while until failure.

    One thing that is worth mentioning is that-
    A) Any 5year old PSU has probably reached the end of its lifespan, especially if it's been used a lot.
    B) Thermaltake aren't a brand that inspires confidence. In fact the phrase "5 year old Thermaltake" is a concern. I don't know which model you have (they have some good ones too) but if its say a TR2 700W then you should probably just bin it.

    While it doesn't really explain the inconsistency, PSUs do wear over time (capacitors etc) and if it is in fact a weaker PSU to start with, it might just be on its last legs.

    If however, you find that the 350W PSU causes you problems too (if its only been a day or so it might not be long enough to induce an issue) then it might be that the motherboard power regulation is at fault.
  2. Thanks for the reply.

    I know its a weird problem. I worked on many pc's and never came across one that would only abruptly shutdown after after installing Windows. I left it run in the BIOS and the voltages where good.

    The 5 year old PSU is a Thermaltake Toughpower 700w p/n:W0106RU.

    I turned my pc on today and got a black screen with just a mouse cursor. I had to reset the pc and then it booted fine. Could I have a hard drive problem? I read about Windows 8 having a fast boot feature, maybe thats not working with my hard drive.

    Asus utility to monitor temps and voltages show everything to be good.
  3. Yeah I'm afraid I don't have many ideas. One thing I did consider is that an older system might be using different voltages, but we are talking an awfully long time ago now.

    It is starting to sound more like a HDD problem. Is it a new HDD? Windows8 is still something I'm avoiding like the plague so I don't really have any experience with any of the quirks it might present.

    When you say you turned on the PC and just got a black screen, is that the second it starts? Or does it show the post screen?
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