I need help with my PC; Windows or hardware issue???

Last week, I had an issue with Windows 7 booting slow and the network not starting up. I fixed that problem using system restore and cleaning the hard drive and registry. After that, everything was working again, but the network still took longer than usual to start. I was suspecting that something was wrong. Then a few hours ago, my PC unexplainably rebooted itself several times and sometimes got to the point when Windows would not boot up at all. OK, so I was thinking that the PSU went bad. I checked the power connectors and fans; fans worked fine and CoreTemp showed my CPU running at normal operating temperatures. OK, so I reinstalled Windows from my recovery partition. PC restarts kept on going! Windows Experience Index was not detecting my video card. OK, so then I installed the Windows 8 upgrade. After booting up Windows 8, the PC stopped rebooting itself, so it seems that I can rule out any issues with the PSU. Then I ran the WEI again and it gave me a low graphics score. I was thinking bad video card, so I unplugged the power connector and plugged it back in. I rebooted the PC. EVGA Precision X started up this time and I reran the WEI. Scores are back to normal and Windows self-installed the 335.23 WHQL driver. So my video card is OK. Now that it seems that my hardware is fine, but when I started to download Windows updates, the PC froze up. Had to do a hard power reset. Now I'm installing a few updates at a time and will keep doing so until I get the Windows 8.1 Update 1 version. What has caused the issue with my PC? Was it a bad video driver (I was on 337.88 WHQL), viruses (my recent scans detected nothing), loose PSU connection, faulty RAM, or possibly the motherboard / CPU? I certainly would hate to wait four months until the Haswell-E CPUs are released, but if the video card is causing problems, then I have no problem upgrading to a GTX 770. Could it be that my Windows recovery partition was corrupted and I can no longer use Windows 7? What's going on here? I need to get to the root of the issue. I would like to stay on Windows 7, but I can't do that with these issues occurring, even after a clean install. Hell, Windows would not even detect the system disk image stored on a USB hard drive.
 
The video card is not stressing the PSU too much; the PC will draw up to about 400w on full load. I'll try running a few games on it and see what happens. I had the PSU for barely over six months, so I don't see how it can go bad now.

But it seems as if a clean Windows 8 upgrade is like a clean Windows install since I am erasing the hard drive during the process. Is it worth it to format the hard drive and purchase a full Windows 8.1 license rather than using my upgrade license to resolve all issues once and for all?
 
I installed Windows 8.1, but cannot sign in to my Microsoft account. My tablet signs in just fine, though. I spent a few hours on a live chat with a Microsoft support tech, but could not resolve the issue. A higher tier technician will call back tomorrow. I reinstalled Windows 7 from recovery DVD discs made in 2011, NOT the recovery partition, which apparently was corrupted. Windows 7 started running fine again, but after trying to reinstall Windows 8, I still cannot sign in to my account. So I cancelled the Windows 8 installation for now. And I still cannot restore my hard drive from a system image. Should I still try to fight through the Windows 8 sign-in issue or just reinstall programs and updates on Windows 7? My personal stuff and games are stored on my HDD, so they are fine. I just need to reinstall Origin and uPlay as well as my Logitech drivers.

UPDATE: I finally got Acronis TrueImage to restore the February 2014 disk image, so mostly all my programs are installed. Most of them will need updating, though, but Origin is running fine. I will need to reinstall OneDrive, though. But I shouldn't be doing too much, though, since I will try to reinstall Windows 8 later. If need be, I will reinstall Windows 7 and get my PC fully recovered. Wish me luck.
 
After updating some programs, after some time, the PC shut itself and rebooted again!! I guess the disk image was corrupted, too. WHAT IS HAPPENING TO MY PC??!?!?! IS IT DYING??!??!!? DO I HAVE TO RESTORE WINDOWS 7 FROM THE RECOVERY DISCS AND REINSTALL EVERYTHING??!??!?! DO I HAVE TO FORMAT THE HARD DRIVE AND GET A FULL WINDOWS 8.1 LICENSE???!?!?! HELP!!!!!!!!!!!!!
 
Sorry for the multiple posting, but I am reporting that the reboots were happening on Windows 8 as well. So I am zeroing in on the PSU as the prime suspect. I swapped it out with my original PSU for the time being, just enough to run my components at about 75-80% load. My best hope is that the PSU was indeed the culprit of the massive problems I was having since last night. I will try to fix the sign-in issue with Windows 8 and if it's not resolved, then I will reinstall Windows 7 and restore my disk image backup. Now when my network connection failed to boot at random times, was it because the faulty PSU was not providing enough power to the motherboard and hard drive? The PSU is under warranty. I heard that the Corsair CX series PSUs suffer from capacitor failures, which may have happened. Should I get a warranty replacement or just get a new replacement unit? I'm looking for a 600w gold-certified PSU, such as a Seasonic or Antec, which is not too pricey, yet has excellent quality. If the PC still reboots itself, could it be because of a bad hard drive or motherboard?