So you're thinking about a new PC

First let me tell you my decision making method for my own computers. I expect 3 years service out of a computer (& basically spend whatever is needed to keep it running for those 3 years if anything does go wrong). After that I'm looking for an excuse to change it (e.g. it wont run a program or game, it'd cost more than $150 to fix or i want to treat myself to something shinny with racing stripes ... if times are, hard an excuse has to be a bloody good 1 (but i still wouldn't waste money on fixing it it it was going to cost me more than say $200 ... .I'd make do until i could afford a new system).
Next, I'll state the obvious - you get what you pay for. While i don't often recommend going for really top of the line equipment (where you pay for the gimmick factor) I'd always recommend going for mid-range or 1 up from mid-range. I don't build cheap & nasty systems - I simply don't want the comebacks; if 1 PC is $500 cheaper than the other .... where has the money been saved, do you really think it hacked off their profits? ... er no ! They've saved the money by spending less money, yes bulk buying will save a fair chunk, but not that much.

Next:- Laptop, Factory Built PC or Custom Build

• Laptop

  I'd only recommend a Laptop to someone who needs the portability or really doesn't have the space for a PC in their home. Laptops are slower (faster needs more power, gives off more heat & uses the battery up quicker) are more expensive to keep running (if a monitor or keyboard on a Desktop PC fails you buy a new 1 , plug it in, job done - not the case with a laptop) & they are a pain in the ass to work on for more than the most basic hardware fixes.
  If you buy a laptop through me I would discuss your requirements & budget & recommend the Laptop most suited to you based on my experience & knowledge as a computer technician, if you buy 1 from a high street store you'd get at best a recommendation from a salesman (that's assuming they wouldn't be trying to flog you whatever was currently most profitable for them).

• Factory Built PC

  If you know what you're doing, have basic requirements & don't mind doing the setup yourself (run the install, uninstall all of the crapware that comes pre-installed & install your own good programs) factory built systems can be an economical way of buying a PC.
  Factors to bear in mind, don't just go on speed & sizes, the motherboard is the most important component as far as 'out of warranty' failures go & is most often overlooked.
  I personally dislike the 'all in one' PCs in most considerations the suffer the same down sides as the Laptops, but some people love them & as long as failures happen within warranty, it isn't your problem (aside from being without it while its awaiting repair).
  1 final point, small form factor PCs (the miniature PCs) have non standard parts (prime example is the Power Supply) if 1 of these fails once out of warranty 1 of the same exact size, shape & equal or greater power has to be found (more often than not from overseas) rather than my usual "yeah, I've got 2 of those in the van". While I can supply these, unless you're going to do the setup yourself (not difficult but it is tedious & time consuming) they aren't much cheaper than 1 of my basic Custom Built systems (the price of which already includes the setup up cost).

• Custom Build

  Ok, to have a car or bike custom built would cost a ridiculous amount, not the case with custom built PCs (well OK, i do have 1 with liquid cooling, 6 core processor, solid state drive etc, but we wont go there - unless you want to).
  If i build you a PC we have a chat (in person or over the phone) & I glean from you what you need, can afford & recommend the collection of components most suited to your use. While I'll always recommend a good motherboard we might be able to save a couple of $100s on the processor still the same good brand; just a slower more basic processor (if you don't need the extra oomph).... while this saves money, it makes the PC no less reliable.
  Things to consider how many USB's will you want, on-board (built in) graphics or a graphics card (& how good a graphics card) how many hard drives will you end up fitting, will you be over clocking (tuning up) your PC - then you need to think about case design & cooling system, do you want a second DVD Drive (or do you want blue ray), extra drives (or an SSD - super fast drive), TV Capture Card, state of the art sound card ........ (i think i best stop there).

Finally:- Software

OK, so what is Software? Software & hardware can be very easily distinguished by a very simple method. If you can literally put your finger on a part of the computer (dismantling it as necessary to get at it) then it 's hardware, if you cannot, then its software. While you can put your finger on your Microsoft Office install disk, you can't put your finger on Word or Excel (so the disk is hardware, the programs on it are software).

• Operating System

  The operating system is to the computer like a conductor is to an orchestra ... it gives permission to a specific instrument to 'do it's thing' at a specific moment. Ok, so that's as clear as Shinola. Some examples of Operating systems are Windows 7, Windows XP, OSX Mavericks, Debian & Windows Server 2012 .... so its the conductor that allows programs like you anti-virus, office suites, browsers, web cams, do what anti-virus, office suites, browsers, web cams do, at a time that works with everything else.
  Windows XP has recently (at time of writing) ended its amazingly long lease of life, some older systems still run Vista, but currently you have a choice between Windows 8.1 & Windows 7, I will now be as tactful as I can be & simply say that I don't like Windows 8.1 & while I would gladly build a system with it I wouldn't recommend it to anyone (& have so far not built a single system for a customer with it installed).

• Other Software

  So now you have your computer with an Operating System - a guy with a baton isn't too interesting on his own, now its time to set up the band.
  Office suite, Pdf Reader, Picture editing software, a decent Browser (with flash installed), A good video player, a music player, a decent browser, & you'll want good antivirus program PLUS any other programs you'll want to make your computer FUN.