Wanting to upgrade Power Supply, please help!

Hi! I am somewhat new to these forums, but I have been lurking some so I hope I am in the right place. A little about my background.

I have a older machine. It is an emachines W4685. Up until about 3 months ago, it has been an excellent little machine. I play a few graphics heavy games and do some work with my photos on it and it was able to handle it all with no problems. About 3 months ago, it crashed. I had to completely reinstall Windows and I though that fixed the problem. Then, about 2 weeks ago, I started getting BSOD, but they were never consistent. Always different. I really think I have had just about every one I could have. I have changed my ram with two new sticks from
Crucial and changed the CMOS battery. I have tried several different programs and the ram is perfect. The past couple of days, I haven't been able to log into my computer at all. The first obstacle I was presented with was system32 was missing or corrupt. I was able to recover from that and get back into windows. But, each time, I am only able to get to the Windows welcome screen. It either gives me a BSOD or reboots. I do not have a lot of specifics, but I can remember some specs about my computer.

emachines W4685
Pentium 4 processor
2.6 Ghz
2 GB ram

From what I have gathered around the net, it could be a number of problems. The one that really sticks out to me is the power supply. What do you all think? If it is the power supply, what can I upgrade to. I have a Bestec ATX-300-12e. Any help is appreciated. Right now, I am using a friends laptop. My computer is just taking up space. Will a new power supply help or could it be something else? Should I save myself the headache and just get a newer, better syste? I am pulling my hair out!

First thing that you should do is to scan the hdd for the bad sectors.