I'm sorry, but I'm not going to buy a new computer just yet. 8 years might look like a lot, but it still works and I know that with some fine tuning (upgrading RAM, for example) I can make it run smoothly again. I'm not falling into consumerism, sorry, there's no real need to buy a new computer.
I know that it won't work with new technology, actually it's kind of better because old technology is cheaper.
Also, my computer cannot run DDR3 RAM, but it can run DDR2 RAM, and from where I'm standing, it looks pretty good.
By the way, my computer was really expensive and to renew it, it would cost a ton of money, so it's not an option. Maybe my Mac Mini will be replaced with a new one soon, but my main computer (the Mac Pro) isn't. This is because upgrading my Mac Mini isn't worth it, I'd better buy a new one. In the other hand though, upgrading my Mac Pro is definitely a good option. Also I'd like to state that ALL my files are backed up, so no problem if my computer stops working. Either way the internal hard drives can be removed so there would be no problem.
Anyways, thanks for all the help! If I ever go for a custom PC, I'll let you know!
If you can help me further, I would appreciate it, but keep in mind that I will not buy a new computer just yet.