Ok, starting about a week ago, When I try to restart my computer it will go through the shut down process, get to the screen where it's at the point of restarting, but instead the screen goes black and says 'Auto Detect, Entering Power Save Mode". From that point the PC will just hang, and not restart. The only way I can 'restart' my pc is by doing a 'cold boot' /pressing the power button. Mind you, my computer will 'shut down' just fine, however, when I try to restart windows, it will not, and go into powersave mode. Initially I thought this was a problem with a corrupt file of some sort and end up doing a zero fill yesterday. Reinstalled windows, everything worked fine, pc restarted without 'hanging', however it is starting to do the same thing again, won't restart. I'm leaning towards my Power Supply Unit being at fault here but I'm really unsure and need a second opinion before I purchase a new power supply.
EDIT: While I was just browsing the web my Monitor went into 'Powersave Mode" and won't come out of it, so this isn't just a 'restart' issue.
Monitor: Dell E248WFP (Purchased Jan 08)
Power Supply: Thermaltake 650W (Purchased Dec 07)
So both are fairly new...what could be the problem?

Hi welcome to PCHF when you restart and it hangs is the power light and hard drive light on the front of the PC flashing and on?

Hi, I can't see a light indicator on my HDD at the front of my pc, but on the power button, yes it does blink. I no longer even believe this is a 'restart' issue. I was just browsing the web an hour ago, and my computer went into power save mode again. I cold booted my pc, turned it back on...few minutes later it goes back into power save mode.

have you tried turning power save mode off? in the power option in the control panel to see if it works properly with power save turned off.

Yeah I tried and that doesn't help, still does the same thing.