Do I have a bad CPU, MB or PSU?

I know a good deal about PC hardware but this is driving me crazy. I have a PC that I built over a year ago that's giving me major problems now. Everything was great until one day a week ago, my computer shut down. Almost to a standby state. My monitor went out but my fan on my CPU went full blast. I couldn't get it to come back on besides hard booting. I logged back into Windows with no issues thinking it was a fluke. Then a few hours later, it did it again. Monitor went out, fan speed increased, had to hard boot. My PC is NOT set to go on standby ever. Neither is my monitor. It's set to Always On. I even adjusted some sleep options in BIOS switching from S1, S3 to Auto and the issues persisted. I checked the temp on my duo core Pentium chip and the temp was at a reasonable 40-50 degrees Celsius. My mb was also running at that temp. I even downloaded an app to monitor the temp of my gpu and it ran at about 60 degrees. My cpu utilization was not being maxed or anywhere close to it. I ignored it hoping it would go away and it did it again. I shut it down and haven't been able to turn it back on. I get a beep code (1 long, 3 short) with an AMI bios. A quick search said that beep code results in faulty memory. I reseated all sticks (3 sticks, total of 2gb). Same, wouldn't boot w/ same beep code. Tried each stick individually. Same. Tried them each in different slots, nothing. I seriously doubt that I have 3 bad sticks of ram. I booted with the case open and everything turns on when I boot. At least the fans and devices. Not sure where to go from here. I don't have another CPU, MB or PSU to test and I really don't feel like buying a whole new set if the problem is being caused by just one or something else all together. Any ideas? I've Googled my tail off with no clear answers expect to replace each device. That doesn't help. Thanks for your time.