Windows Vista Computer Will Not Start Up

Ok I have a bit of a problem with my Windows Vista Computer. I have had it for I believe two years now and have had no problems with it whatsoever, it has worked fine, haven't had any errors or anything, until recently. A couple days ago my computer started to run a little slower, and at one point it ran real choppy, gave me a blue screen, and made me reboot. Once I rebooted I had to turn my computer on and off several times to get it to work.
It worked good for about 2 days, and then it happened again, except this time it took longer to reboot. Once again, it seemed to work fine, and I became a little concerned and I tried looking up some sort of solution to fix this problem and was about to reinstall the operating system when it crashed again. This time, though, it won't start up no matter what I do, and I try the windows fix option, but it goes into the loading screen, and shuts off once it reaches the end of the loading bar every single time. Im guessing its some sort of hardware error, and something in my computer is either broken or just loose.
Does anyone have any idea of what is wrong with my computer? I will list some information below, but Im not very computer savy so i don't really know if this will help or not. . .

I am using. . .
*Windows Vista Home Premium
*Emachines Computer Model T5234
* Graphics are powered by Nvidia GeForce 6150SE
* AMD Athlon 64x2 Processor 4000+
*DVD+_RW Super Multi-Format Dual Layer Optical Drive
* 320 GB harddrive
* 1 GB DDR2 Dual Channel
* 15-in-1 Memory Card Reader

So far all I have tried is turning it on/off, unplugging the computer and restarting it, leaving it unplugged for several days and restarting it, trying to reinstall the operating system (it started to load, then failed), unplugging the keyboard/mouse/printer in case of a hardware error.

Any Help will be greatly appreciated! I really don't want to have to buy another computer. If you need anything else to help me define this problem please tell me and I will do my best to help!