First of all, hi and welcome, and dont worry because we all started like you a while ago.
Can i ask what monitor you have? Is it old, and what is the resolution (if you know it)?
I ask because, just like the insides of a PC, the external stuff is in constant development and although you might be happy with what you have, you might surprise yourself with what you could upgrade to given your budget.
As an example, you might be happy with a 17" 1280 x 1024 monitor, but find that you could afford a 24" 1920 x 1200 one instead.
Same with speakers.
Just an idea.
The second point is to consider what physical size PC you want or would be happy to have. There is a mid-point, above which cases get very large (and costly) and below which they get nice and small (and costly!).
Also consider noise - you might be used to a fairly noisy PC and suddenly be delighted with something near-silent. Then again, you could be expecting quiet but end up with an uncomfortable jet-turbine sitting next to you, if you pick the wrong bits.
A final point to ask is whether or not power consumption is a factor - i'll be honest, it's not for most people, but you might be a) an eco warrior in disguise or b) thinking about the ever-rising rising electric bills, like me
I'll post some suggestions of specific parts if you want, but let us know about the above first