The OP is nearly computer illiterate so go easy on him. Basically guy, you need an entirely new computer. That's right, all new hardware. This is what everyone has been trying to tell you. "Amp" is a misnomer, it's a Power Supply Unit (PSU) since it's more than just amplification of power. Honestly i've never heard anyone in my entire 20 years of doing computer **** call it an amplifier, once I heard that term used I went 'oh here we go....' lol. I could go into the difference, but it's not the same as an amplifier for your sound processor on an audio unit. Even in audio, more watts does not mean better, in fact that can destroy your speakers if not properly matched. But that's a topic for another thread.
Yeah if you're interested in upgrading your rig many people have already stated what you need, ram, graphics card etc. But really it's a waste of money. The computer you have at the moment isn't worth putting money into, rather an entirely new rig would be where the money is best spent. Your hardware is several generations too old and simply not worth the investment. Save it and put it into something new where you'll get the best bang for your buck.
Now i would not suggest actually building your own until you've spent the time into learning the different functions and so forth which can take years (yes you head me, years if you're starting fresh). I doubt you want to do that so just buy a new one pre-built and ready to go.
Also, stay away from e-machines. Just....stay away, far away. They use the cheapest of cheap crap into them and they're junk. **** even a dell or hp would be much better than e-machines.