Windows 7 turns off itself

hi let me be neat. I clean reinstalled windows 7 home premium a few days ago. At first I forgot to turn off hibernation in power management, when the PC was left alone for some time it turned off but it could never be waken up again with any press on keyboard. I couldn't even turn on the PC when I switched off the main wall socket and switched back. The PC was like dead. (No lights at all). Later on, I didn't know why, the PC could be turned on again and boot to Windows.

At first I thought it was about hibernation problem, then I turned off the hibernation (set to NEVER), now the PC does not suddenly turn off after some time BUT it COULD still turn off at random time. Yesterday the whole screen suddenly went black and all lights on the chassis went off again. Lights off, fans off. Once again, it couldn't be turned on (EVEN IF I switched off the main ac and switched on again) , I had tried for a long time but never figured out the reasons.

Then I unplugged the USB of the mouse and keyboards and portable harddrives from the PC, then the computer could be turned on and boot to windows again!

My friends are not computer experts but they guess that it's about the problem of PSU but I don't really agree. It's a decent and 100% authentic Antec PSU which was bought only in late 2013 from a trusted vendor. I don't use any graphic card and CPU was i5 only. I only have one hard drive so I don't think it's the problem of power.

My question is

1. Why it happen? Could anyone help guess? How can I troubleshoot the problem by myself?
2. On the other hand, the speed of my computer has become very abnormal. I am using a quality 100MB high speed broadband but I can't load a random ordinary webpage for hours. I guess it's not the problem of the ISP but my PC

3. After all, do you have any ideas on what I can do now?

mitchell65 said:

Sounds like your PC is infected with a virus. What anti virus are you running and is it up to date?
Please complete your system specs so that we can help you more, see here:
System Info - See Your System Specs

Kaspersky and Avaxxx (I forget how to spell). I have known for long that EXE files from untrusted site are never opened and I never use crack or patch files and I always use authentic and legal software

Kaspersky and Avaxxx return with 35 threats after scan, but no virus. I think it doesn't make sense. The threats are all HTML files which were websites saved under Yahoo! Domain. I don't think there is any virus or real threats.

badger906 said:

a virus will not affect the computers ability to turn on or off. the OP has stated it wont turn on EVEN after unpluged from the mains, this would kill any windows hibernation files and resort the computer to being off.

99.9% of the time virus do nothing other than piss you off or steal your stuff.. its safe to say this is NOT a virus :)

this is almost definitely as stated by your friends a power supply issue.

the reason it doesn't turn back on would be the capacitors still holding charge and thus causing the psu to still think its on, so no matter if you press the power button it wont do anything.

again unplugging it at the wall wont always solve it as if its still holding charge the same affect occours.

for arguments sake check in tbe bios theres no option for usb control in hibernation/sleep, as some bios have a power off and on usb feature.

the only real test is to try a new psu.. it will still be in warranty if you cant borrow one, so sending it back for a replacement is an option and at worst if its not the psu and actually a mobo fault youll still have a snazzy new psu!

I guess PSU the least likely to be the problem. Because when I bought the hardware last year I followed th my friends' advice that I spent the most on PSU, that's Antec 400W. The motherboard is ASUS but a low-end one. The CPU is Intel i5 2400 (Old CPU). Hard drive is Seagate and is new. I don't install any Graphics card at all. The Ram is Kingston.

Sending back the PSU? If PSU is tested to be no problem will they send a new one back to me?

But I guess the problem is the MOBO. I am not sure. Because I once dropped a screwdriver (accidentally) to the MOBO during the computer build

badger906 said:

the OP has stated it wont turn on EVEN after unpluged from the mains, this would kill any windows hibernation files and resort the computer to being off.

That's not true, hibernate works even if the power goes out ... that is what it is designed for
Sleep and hibernation: frequently asked questions

It certainly could be a PSU issue ...

If I had this issue I would check if there is new BIOS version for the motherboard.
I would also check the MB forum to see if others have reported similar problems for this MB ...
Perhaps even a BIOS reset is needed.
If you're overclocking, don't ...

Layback Bear said:

Is their something wrong with my browser.
I still don't see the OP System Specs as requested twice.

Sorry, I have already followed the instruction and filled out the System Specs