So I went the lazy route and rather than go for a clean install this time around, I decided to try the Upgrade and keep all programs/settings. After two failed upgrades that hung at 97%, I finally got Win8 installed. For the first couple hours everything ran fine. I uninstalled a bunch of old unnecessary programs, ran cccleaner, defraggler, updated my drivers, etc. I then installed a couple updates that needed to restart my PC. This is where the problems started.

1.) Every time I boot my PC It goes from the boot logo, to a black screen where my backlight shuts off on my monitor and it hangs there for a few minutes before booting.
2.) On shutdown it goes to a black screen with my cursor and hangs there for a very long time, then on the next startup says it didn't shut down properly.
3.) Playing any of my games for more than 5 minutes causes Win8 to crash and reboot.

I have run sfc and got no errors, Ive tried running chkdsk 2x and I get stuck at 27%. I ran a couple programs to check for errors in my HDD and have found none.
I went from Win7 64-bit Ultimate to Win8 Pro. Both OS were legitimately purchased.
CPU: AMD Athlon II x4 645
Graphics: GTX 560 (OC)
RAM: 6GB DDR3 @ 1333MHz

so my specs are definitely good enough

Has anyone else encountered these issues, and if so, does anyone know any fixes?